It's nice but nothing great, definitely nothing WoW has to worry about. The game interface is just clunky compared to WoW, though part of that is thanks to add-ons, but Blizzard at least had the foresight to enable add-on support. If the controls aren't fun then no one will enjoy playing, no matter how pretty.
The story is non-existent, some city is named Pandemonium, angels vs. demons battling for territory and then teaming up against actual baddies, yeah pretty trite stuff. At least with WoW the story is actually extremely developed, and there's plenty of comic relief outside the lore cut scenes cinematics.
My biggest problem with it is just how much it tries to be like WoW, but only gets it on the surface. Granted I'm going off only a few minutes experience, but if I get turned off that fast, it should say something. I immediately loved Ragnarok, Sword, and Atlantica. The starter zone for the Elyos looks basically like Elywnn Forest. People need supplies moved from a farm, there's too many of this animal, etc. There's even a pig finding quest, and there are several of those in the Elywnn zone in WoW.
It just seems all style, no substance.
-It plays very smoothly, as in the graphics rendering, but maybe a little too smoothly.
-There is basically Sims-grade character customization
-It's WoW with a Korean makeover
-Customization is more enticing than playing
-No support for user changes
Granted a more in depth comparison by someone who has experienced both endgames will probably persuade more people, but for the average WoW fan who is curious, don't waste your time or bandwidth on this 9gb download. The Sims 3 is cheaper, too.