It's actually a pretty fun game. The game feels more like a giant amusement park, essentially everything, even combat is considered a mini-game, except without the long lines. Basically combat is divided into little encounters or small to medium sized dungeons. One encounter might have you go off against 15 or so enemies, others might have you go up against 3 powerful enemies and a mini-boss'ish mob. Each encounter has a difficulty rating based on your level to see if you may or may not need an ally to go with you. I haven't tried any of the kart racing or demolition derby stuff yet but it looks fun.
A lot of the content is free yet there is a premium monthly service that gives you access to more quests, items, dungeons and classes(mostly combat classes). You can change classes at any time except during a mini-game/encounter. If you don't have a combat class selected when you go into one it'll ask you to pick one and then let you enter. The initial download is pretty light but the game streams new areas as you explore and new content is added on the fly so your install will get significantly bigger over time, it does a pretty good job of streaming stuff in so you generally don't have to wait for an area to load unless it's the first time you enter a long dungeon. The handiest thing are the teleport stones all over the world map that instantly let you get to places for free so no down time. Plus there's a feature to allow you to warp to friend's position from anywhere.
My only true gripe is that the interface has a lot on it and takes a bit to get used to and they throw a lot at you at the beginning, mostly I guess to see which aspects of the game you like.