The Rifts add a nice touch to the boring generic MMOs. Though the rest of the game is generic as can be. Thus, I find it better than WoW, except leveling.
Leveling is slower than WoW's and it feels like I have to run back and forth within the map to recieve and complete quests which gets heavily annoying.
Major/Minor rifts (Which are by far the best way to gain EXP, you gain its and very fast) don't appear enough IMO.
Rift Invasions are fun, TONS of rifts appear all over the map and thus you can gain lots of experience very quickly.
In WoW, the "fun" only comes from dungeons. Rifts you'll see all the way through leveling and they are like public raids.
I'll be waiting for Guild Wars 2 though. There version of GW2's event system doesn't seem as amazing. There's only like 4 types of rifts so it's basically the same monsters over and over.
Conlusion: It's a WoW clone (And I never use that term) with Rifts. If you like WoW, you'll like this more unless you hate dynamic-ness.