I was in the beta, so here's a few thoughts on the game and why I'll not be buying it. These are all half-remembered points, so take them with a pinch of salt. (Btw I played a berserker I think... If you do decide to get the game you should play one too. Best class)
Firstly, the combat is really really well done. Like seriously fun. You're dodging and blocking and watching the enemies to see what they're doing... It works really well.
Unfortunatly for some reason you spend the first 20 or so levels fighting monsters that barely even put up a fight. Pretty soon you realise that you don't have to block and dodge and such. I could literally jump into a group of enemies, start swinging wildly, and then come out barely hurt. I think I died once the entire time. I dunno if this is some extended tutorial or something, but it really felt like they were mis-handeling the awesome combat system they have. It does get better after that, but it seemed like the game was doing the oldschool MMO thing of "group up or fuck off" because enemies became way harder, with huge pools of HP. I think it was taking the better part of ten minutes to solo one mob. Which leads me to my next point.
The rest of the game is like such a throwback to horrible MMO design of yore. Every quest is a generic MMO quest. Most of them are kill X monsters. The game in general just felt like it was full of grind, which is definatly not my thing. When a quest is telling you to kill 15 monsters, each taking either a full group or 10 minutes each, and you have a quest log full of that exact quest with different monsters, it gets kind of tedious.
There also seemed to be a strict progression track, with generally only one zone for each level bracket. Which basically means if you're playing a second and third character you'd better be prepared for the same content over and over. This is something that I just can't stand in MMOs, as I like to try out a few different characters.
There's some sort of a system for enchanting your weapons, or upgrading them, or something. Basically you pick up a magic weapon and it'll say "+3 effect X/+6 effect Y/+9 effect z." So you have to upgrade something 9 times to get all it's effects and such. To upgrade your items you need to use another item of the same quality and type, so level 14 sword to upgrade a level 14 sword. This can fail, which loses you the item you're using to upgrade. When it fails it can also knock you down an upgrade level. Random chance is bad enough, but the whole losing enchantment levels is just asenine. Bearing in mind from what I can tell this was EVERY magic item above white on the MMO colour-quality scale.
I should also probobly mention the underage animal girl race. Solely because there wasn't 10 minutes gone by without someone bringing them up in the main chat channel. If you find the idea of sexualised children characters in a video game to be creepy stay far away from this game. If the time I spent playing is any indication your time in TERA will be filled with people saying how "delicious" their pre-teen cat-ears girl avatar is, or other generally really creepy shit. It'd be tolerable if it didn't dominate pretty much every conversation in the chatbox.
There's a few other annoyances, but those are the main things I remember turning me off the game. It's really quite a shame that such a terribly designed MMO has some of the best combat I've seen in the genre. As I said, I might have misremembered parts of this, it's been a while since I played, but it's definatly not avoided MMO cliches at all from what I can remember. If you've got a few freinds and just wanna roll around an MMO in a group this might be worthwhile just for the combat alone. But so much of the rest of the game is just the worst MMO game design.