I've been playing since launch, and I'm still using the turtle mount from the collector's edition (kuripot ako). I have a level 50 pyro/chloro/stormcaller, but I am (or was) having more fun with my rogue (saboteur main) until around level 30ish.
The game is alright. If you also played Warhammer Online, the tiered battlegrounds, tiered dungeons and gears, and invasions and rifts (the concept of which was taken from Warhammer's Public Quests) will be very similar, and that may either be good or bad.
Truly, the game's selling point is the depth of the customization. With the ability to acquire all the souls (specializations) and purchase several roles (one role is a combination of any of 9 or 10 souls available to your class), the possibilities are myriad indeed. And you won't have to repeat a class just because you want to try something else. For example, you have a rogue that deals damage and you want to try a rogue that can tank (yes, rogues can tank in this game via pumped up evasion skills), you won't have to start from level 1. You can just purchase a new role.
The game started with like more than a hundred shards (servers). But the subscriber base is settling down now, and they're starting to merge servers.
Is it a WoW killer? Well, of all the MMORPGs released so far, this one was the game that seriously put a dent on WoW's subscriber base (a 1.2 million decrease in WoW's number of subscriber coincided with Rift's first 2 months of release).
But no, in my opinion, it's not the WoW killer that people have been looking for, and some have been desperately waiting for.
In my WoW guild, around 5 or 6 people quit when Rift was launched. They're back in WoW now, raiding the Throne of the Four Winds.
I'm one of them, lol.
