I feel like a lot of people are hating on GW2 because there are so many videos with terrible gameplay like http://www.youtube.com/watch?v=lCKnoyYd7oo&hd=1 and people just assume it's another WoW clone dumbed down with only 10 skills usable at a time which is what I thought about it too initially when I played TERA. Tera's combat isn't good compared to other action type games that it's similar to Ninja Gaiden, other hack'n slash action games or fighting games in general. It's just too slow paced. Comparatively, GW2 offers the same action combat but differently, most notably without animation rooting. It's a hybrid between mouse target and the action based gameplay that Tera has. The mouse target I don't mind since most action games have targeting systems anyway, but the action part of it can't really be seen unless you watch videos of really good players. Here's my favourite example: http://www.youtube.com/watch?v=RR0-S9SQCW4&hd=1
at 3:20 you can see the level 6 I think warrior fights an elite monster that is level 11 and kills him without getting hit once. If he did, it would probably have 1 shot him. A level 11 guardian tries to help him out and tank damage and then dies. Skill based combat proven. Another really great video that shows the devs playing, they are really good at the game. http://www.youtube.com/watch?v=OYXpLDcfkdY&hd=1
PvE can be difficult as one of the devs points out, as he dies to one hit from a monster his own level. In Tera, at level 30 I could easily take 10+ enemies five levels higher then me, take multiple hits from them and not die as a leather armour class. Some really great PvP at 22:50, mesmers look really fun to play, and hard to use. From what I've heard a lot of people are complaining they do little damage, but this is probably due to how you need to use your clones perfectly and stay at optimal range if you want to dps well don't just hurr spam clones and let them attack enemy while running close up with your greatsword as I've seen in almost every other mesmer video.

I already prepurchased and will be playing in the beta next week. Kind of hoping it releases before Diablo 3 because I know that I'll buy D3 ASAP if it's not out yet.