There are two Universal parks in Orlando, Universal Studios and Islands of Adventure- this review is about the former. A third Universal theme park called Epic is coming soon! Universal Studios is a ton of fun, especially because it is a lot less crowded than Islands of Adventure and the lines are shorter, often non-existent! Universal Studios isn't as beautiful as some of the Disney parks, but the Harry Potter area, Diagon Alley, is gorgeous and the rides in the park are great! Arrive as early as you can- 8:15am to the parking lot. They will let you in a little early and you can enjoy the park with near-empty streets! Everyone rushes to Diagon Alley to take the Escape from the Gringotts ride, a high-speed 3D rollercoaster (must be 42" to ride). It's a good idea to catch it early since the line is long later in the day. The queue area is beautiful and magical, with animatronic gringotts to see. The ride is quite jerky, though the story is exciting and the 3D aspect makes it seem quite real. This ride has a single rider option so you can skip the regular line if you don't mind riding alone. 

Diagon Alley, the Harry Potter land, is a masterpiece and it's a joy to just walk around and take in the sights. The architecture is amazing and there are cute shops, sculptures, and details everywhere. You will want to spend plenty of time here just absorbing the palpable atmosphere. It really feels like you're in the book, especially with all the visitors around who are dressed in ties and cloaks. Look into all the windows for some surprises. At sunset it looks especially amazing with the moon and clouds adding atmosphere. Wait to see the dragon breath a ball of fire. Also in the London area, take the Hogswart Express train to Islands of Adventure, if you have a pass that allows you to visit both theme parks in a day. The station is wonderful to behold, and the train ride is full of realistic surprises, though the line can be very claustrophobic at the beginning where you must show your ticket again. 
Despicable Me Minion Mayhem (kids must be 40" to ride) is one of those horrible, jerky rides. If you don't like jerky rides or don't want a sore neck and headache for days after your visit, take one of the stationary seats and enjoy the visuals, which are impressive. I wish I had done this!
Skull Island Reign of Kong (must be 48" to ride) is a jerky 4D simulator ride in a safari through a primitive island landscape.
Our entire family (5 year old girl, 15 year old boy) liked the E.T. Adventure (must be 34" to ride) ride the best. It's not high-tech like the newer rides but it's full of imagination and beauty! The forest you walk through is gorgeous, and then to fly above the city is a joy. It is far better than the Peter Pan ride that people wait hours for at Disney World's magic Kingdom. And you can ride it over and over because there is a short line! 
The other best ride at Universal is Men in Black Alien Attack (must be 42" to ride)! What fun! You ride past aliens and you get to shoot them and see how many points you can score. The ride spins around but it is not jerky at all, just smooth. My daughter wanted to ride this over and over- we went five times! If you don't have a young child to supervise, you can use the Single Rider option, and skip the line. There are plenty of empty single seats in this ride (because it groups people in threes) so you really won't have to wait at all! Though you won't get the fun of shooting side by side with your companion. This ride requires you to put your belongings in a locker, which is pretty unnecessary and inconvenient.
The Simpsons Ride (must be 40") has a fun, colorful theme, but is extremely jerky and can cause motion sickness for hours. Twirl and Hurl (kids under 46") is a dizzying spinning UFO ride in this area. 
The Transformers 3D ride is another very jerky ride but some kids like how it's jam packed with action. It has a single rider option so you can skip the regular line if you don't mind riding alone. There are two roller coasters at the park, both with the single rider option. Skip Hollywood Rip Ride Rockit (must be 51") if you prefer roller coasters with good head support. The seats have a lap bar not a harness, and the motion at the bottom of the drop can whip you forward then back, especially children just a few inches over the height requirement. Revenge of the Mummy (must be 48") is a themed high-speed rollercoaster, which is fun because you can get your imagination involved. There is real fire, mist, and many animatronics. 
There are several shows. Animal Actors On Location is impressive and enjoyable for all ages, with birds zipping past your head, dogs from real movies performing tricks, and animals of all varieties cavorting about. A Day in the Park with Barney is a musical show for toddlers. Horror Make-Up Show reveals techniques used by horror movie make-up artists. Fear Factor Live is an audience participation show. Shrek 4D is a 3D show with jokes (a bit tiresome to me) and plenty of squirts of water and other surprises. Shrek 4D has stationary seats for pregnant women. Tales of Beedle the Bard is a puppet show of wizarding fairytales held outdoors in Diagon Alley. Ragtime Gals is a show inside the queue of the Race Through New York with Jimmy Fallon ride (40" to ride), a male barbershop quartet, not the best performance in the park- the ride itself is a 4D simulator ride with seats that move, only really worth riding if you're a big Jimmy Fallon fan.
The Blues Brothers Show is a street performance of belted-out blues and rock n roll. Marilyn and the Diamond Bellas is a one or two number song and dance on the street in front of Macy's, with Marilyn Monroe and some really cute 1950s girls. Sing It is a rap and harmony show, on the street where the Blues Brothers perform, that currently has a fantastic Mamma Mia/ABBA medley (it is one of three sets so you never know if you'll get it or not)- the performers are great singers! You encounter performers all over the park, including percussionists dressed as construction workers in the San Francisco area, and a singer with 1920s dancers in the Diagon Alley area.
The 5pm parade has pretty floats and a lively atmosphere, but is quite short. Don't wait around for it, but do watch if you happen to be nearby. During Mardi Gras (February and March) the parade (sometime between 6pm and 7:45pm) is incredible and you must watch! The dancers are good-looking and gorgeously dressed, and the floats are out of this world! Try to catch as many necklaces as you can! Mardi Gras is the best time to come to the park in my opinion. Instead of the usual piped-in movie music that is so tiring, there is jazzy music, or silence sometimes, which is lovely!
There are outdoor live music concerts some nights. Don't miss the fireworks, laser, fountains, and water projection show most nights, around 7pm or later, on the lake in the Central Park area (ask google maps for the Back to the Future Train to find this area). The water fountains are just gorgeous. Too bad the music is horribly loud- bring ear plugs to spare your hearing. After the show, wait ten minutes before exiting so you don't have to walk in the massive crowd.
For little kids, there is a fun play area called Woody Woodpecker's Kidzone. The kiddie rollercoaster, Woody Woodpecker's Nuthouse Coaster (36" to ride, with parent), is a bit too short though it does have a drop and some tight turns. The playground is amazingly fun. There are rope nets to climb way up, huge slides to take down, a deep trampoline ball pit, long punching bags to run around amongst, and there's a water play area. There is shade but it's pretty hot in this area. The nice thing about this Florida park is that most of the lines are inside, so that you aren't roasting up while you're waiting for your ride. The outdoor shows are in big shaded amphitheaters with large fans that keep you cool. It is doable even in early summer, though you will need a lot of sunscreen for walking around because there are hardly any trees.
A fantastic place to sit on a sunny day is the San Francisco area, where there is seating on the water and sea gulls flying by. You really feel like you're in San Francisco, and there is no annoying piped-in music.
At lunchtime, you can walk to CityWalk and choose from high-quality restaurant chains such as Bubba Gump or Hard Rock Cafe. If you eat inside the park, a good choice is Leaky Cauldron, in Diagon Alley, where you can eat British treats like Cottage Pie, in a sumptuous Harry Potter setting. Come early because it gets crowded. Another choice is Louie's Italian Restaurant, a pleasant cafeteria with large arched windows, cold AC, and good pizza and gelato. 
Wear sneakers because you will be walking a lot. And bring a stroller if you have a young child.
The best time of year to come to the park is during Mardi Gras (all of February and March), when the park fills with Mardi Gras characters around 3pm and the parade around 6pm is exquisite. Kids love catching the beads thrown from the floats. It's also the nicest time in the park because the annoying piped-in movie music everywhere is replaced with New Orleans jazz. The weather, too, is usually great but can be cold some days. 
Many people stay in Universal hotels so they can get into the park during special hours, and also be a short walk or free ferry ride from the parks.

Directions

Universal Studios is located at 6000 Universal Blvd, Orlando FL 32819, call (407) 363-8000. The park opens at 9am and closes at varying times, from 6pm-10pm. Buy your tickets online to save time at the entrance. Cost is around $50-100 a day, depending on how many days you buy and if you're a Florida resident. I don't recommend the Park-to-Park ticket because there is plenty to do in one park per day. Single Park Admission for two or three days is the best value. You can return to the park that many times within a 60 day period.
Parking costs $25, but is free at CityWalk after 6pm.

Click on map for interactive view