The obvious comparison here is to Walt Disney World: Universal's the only other theme-park operation in the area that is really trying to play on something approaching Disney's level. They have much, much less real estate, so the scale isn't anywhere near as colossal, but for the visitor, that's not necessarily bad. It's really easy to get around Universal's territory, much easier than in Disney's vast pocket universe.
Universal has a number of renowned big steel looper roller coasters... which I didn't ride. I don't know, maybe I'm slowing down. Part of it, I suppose, is that I was more interested in the park's signature motion-simulator/dark-ride attractions, and they provided more than enough sensory assault for one visit. There were also only two of us adults along to wrangle my 8-year-old daughter. I did ride one very special coaster at Universal, more on which below.
Of course, the big draw here, and certainly the thing that drew us in, is The Wizarding World of Harry Potter. This is an attraction that first opened several years ago at Islands of Adventure, an incredibly detailed representation of Hogwarts Castle and environs in the village of Hogsmeade.
Last year, they opened the other half of it at Universal Studios: Diagon Alley, the hidden wizard neighborhood in London... and connected the two with a functioning Hogwarts Express! My kid has been seriously into J. K. Rowling's Harry Potter books and the movie adaptations for a while now (though she's only gotten as far as Goblet of Fire), so it was the perfect time to bring her.
Wands! Wands! Wands!
We spent much of the first day, and substantial parts of the rest, just hanging around the Harry Potter areas. Both parks are nice-looking places in general, but the theming in these areas is nothing short of incredible, meeting and in some ways exceeding Disney's operation. They had a huge body of familiar source material (that had already been visualized for the movies) to work from, and the fact that Rowling names dozens of magical commercial establishments in Hogsmeade and Diagon Alley probably looked like a license to print money: we can get people to come thousands of miles to visit our souvenir shops!!
And so it is. Every kid who comes here wants to buy a wand, for one thing. Ollivander's Wand Shop is one of the favorite attractions (there are actually two Ollivanders, one in each park), though Ollivander's proper is a little show in which an actor takes one lucky visitor through the wand-selection process, opening into one of the many gift shops where the wands are actually sold. (They're sold pretty much everywhere in there, and also at other places including Orlando International Airport.)
Some of the wands are interactive wands, which will make shop displays animate in cool ways if you stand at various special locations in Hogsmeade and Diagon Alley and cast a spell (Disney's "Wizards of the Magic Kingdom" is, I think, a knockoff of this). We had a lot of fun with this.
I think my favorite bit of theming was the inclusion of Knockturn Alley, the street of dark wizardry just off Diagon Alley. There's a spot in its dim and eldritch reaches where an animated poster displays, among other things, what is identified as the skeleton of a goblin; if you stand in front of it and wave an interactive wand around, you can make the skeleton dance with you.
A particularly clever feature of the Harry Potter areas is that they're now connected by a functioning Hogwarts Express. You can only ride on this if you have park-to-park access that allows you to transfer between Universal Studios and Islands of Adventure, a feature of most vacation package deals. If the lines aren't too bad, the Hogwarts Express actually functions as a convenient means of transit between the two parks, since it connects the areas furthest from the front entrances, and the trip is quite a hike on foot.
It's also a simulator ride in itself. Though it's an actual train, whose termini are styled like Kings Cross Platform 9 3/4 and Hogsmeade Station respectively, it has no actual windows: the exterior windows are video screens showing the voyage between Hogwarts and London, and the frosted-glass compartment partitions on the aisle side have animated character shadows projected on them from outside while the train is moving. Each direction has its own little story. The London to Hogwarts direction is the best: out in the aisle, Harry and his pals encounter an Azkaban Dementor on the train and repel it with a Patronus spell, in a variant of the incident in Prisoner of Azkaban. Meanwhile, you see the Weasleys' feral car skulking in the woods outside. The other way, Ron pulls a prank involving spiders, and the scenery includes centaurs and the Knight Bus.
Harry Potter and the Escape from Gringotts
As part of our package deal, we had "Universal Express Passes", an evil perk allowing us to skip the longest version of the queue on most rides. But it doesn't apply to the big signature rides in the Harry Potter areas. So on the second day we decided to ditch our breakfast reservation at the Leaky Cauldron and get in early on Diagon Alley's new-ish centerpiece, a theatrical indoor roller coaster called Escape from Gringotts.
Escape from Gringotts is set in Gringotts Bank, the goblin-run financial heart of the British wizarding world. In the movies, the ride down to the vaults is depicted as a wild roller-coaster-like experience. Again, adapting this to an actual roller coaster was probably a no-brainer.
People, you must ride this thing if you go to Universal. Considered as a roller coaster, it's a gentle family ride, with nothing worse than a couple of not-very-steep drops in the dark (it has to be, since you're wearing 3D glasses the whole way and they need to stay on). The ride stops and starts for various show elements, and the cars can also rotate from side to side under ride control, but they're not free-spinning and the intent isn't to cause vertigo; it's so that you can be positioned to see the 3D movie scenes along the way. So this is sort of a dark-ride/coaster hybrid.
The theming and dark-ride/simulator aspects are astounding. The queue starts in the ornate lobby of the seemingly half-collapsing Gringotts building, staffed by animatronic goblins (my daughter has a weird phobia of animatronics that didn't register because she thought they were human actors). There's a movie pre-show in which one of the elder Weasleys confronts a goblin with some kind of plot stuff I didn't entirely comprehend (there's some kind of MacGuffin in there? I dunno, it hardly matters. I think I might need to read Deathly Hallows to get it).
Someone unauthorized has gotten into the vaults, and the magical security systems think it might be you, so once you go hurtling into the caverns of the bank, you have to deal with fire-breathing dragons and giant armored trolls blocking your way. There are fire and water-sprinkly effects. There's an excellent moment in which you suddenly tilt forward several degrees and are held there before plummeting into a dark drop, and another in which a giant suit of armor flings you sideways out of the room. Eventually you encounter the real intruders, who are none other than Voldemort and Bellatrix Lestrange! Making this the finest roller coaster I know featuring Helena Bonham Carter.
The 3D video is bright and never headache-inducing, and while there are thrills they're carefully contrived not to be sick-making. The storytelling is slightly muddled, but it's peripheral anyway. For sheer theatrical spectacle this is better than Disney's Expedition Everest.
Harry Potter and the Forbidden Journey
On the last day (for reasons that may become clear later), my daughter had had enough and demanded some downtime at the hotel, and Sam kindly obliged her, leaving me alone to do whatever I wanted for a while (subject to weather: there were off-and-on torrential rain showers all day long). I headed for the Hogsmeade's central signature ride, The Forbidden Journey.
This is a few years older than Escape from Gringotts, but it's still incredibly impressive. However, it's also a more physically and visually intense ride, which many kids won't want to go on. Its queue is basically the most famous sights of the interior of Hogwarts Castle: you see the founders' portraits arguing with each other, the Mirror of Erised, the Fat Lady portrait who guards the Gryffindor common room, the talking Sorting Hat, etc. It makes standing in line for this thing really entertaining, but if I have a criticism of it, it's that some of this really should have been a separate walk-through attraction: these are probably the most iconic sights in the whole park, and many visitors never see them because they don't want to go on this ride. In principle, you could stand in line for the ride and then just ditch at the chicken exit, but I don't suppose many people do that.
Anyway, if you're up to it, The Forbidden Journey is also amazing. This time, the story is a wild ride through the sky around Hogwarts Castle (you're apparently on an enchanted bench), chasing Harry on his broomstick through a Quidditch game against Slytherin and almost colliding with many things. The visuals alternate between (2D) movies projected on curved screens, and traditional dark-ride animatronics (there is a physical Whomping Willow, which is my personal favorite bit).
The ride isn't a roller coaster and doesn't move fast, but the ride seats are actually mounted to the cars by articulated robot arms, so you get lifted up into the air and generally waved about, pointed up at the ceiling and dangled toward the ground. The restraints, therefore, are over-the-shoulder, and you have to be sure to stow loose items. Together with the crazy broomstick-ride visuals, it'd probably turn a lot of people pretty green. This turns out to be a common theme at Universal...
Both Gringotts and Forbidden Journey have instances of a wonderful thing in concept: banks of lockers that can be used for free for the length of the ride (you can pay to rent them for longer). Unfortunately the execution has a flaw: so as to remove the need to carry a key, the lockers are controlled by fingerprint-scanning stations, and those biometric scanners are just not ready for prime time. Strangely, they worked fine for me (I'd been spited by similar scanners at the entrance to Disney's Magic Kingdom), but I saw one poor fellow who had just ridden Forbidden Journey scan his finger five times before he got his locker to open. I got a laugh by announcing it as "Harry Potter and the Lockers of Rejection."
 Crowds turned out to be light enough that, most of the time, queues weren't an issue anyway: Massachusetts' school vacation week is at a slightly unusual time, and it was the middle of the week. I think a large fraction of the people there actually were from Massachusetts.
 The Room With A View Coaster at Six Flags just didn't deliver.