During the Open Beta for Tera (April 20-23) I had a couple hours free to level a slayer and an archer, each to about level 8. The following is my brief reaction.
Take an MMO you've played (WoW, Rift, SWTOR, etc) and remove the targeting system. Instead, aim your attacks with a reticle like a third-person shooter. Ta-daa, you are now playing Tera. It's that simple. Can you circle-strafe? No. Your character must be stationary for the length of the attack/spell-casting animation, even if it's an instant attack. To move you must stop attacking. However, each class has a "dodge" button on about a 7-second cooldown. This is bound to the right mouse button by default (the normal spammable attack is bound to the left mouse button by default). The slayer has a dodge that you can aim with the WASD keys, but the archer's is just an instant backwards leap of about 6 feet. I felt surprisingly immobile. Maybe some of the other classes feel more mobile. Still, I will admit that the combat is somewhat faster than most MMOs, and dealing with groups of enemies is easier due to not having to keep tab-targetting.
Standard MMO fare here. The story quest has some in-game cutscenes now and then, but is mostly "go over here, talk to this guy, read a couple pages of text, kill a monster." The rest of the quests are either tutorial quests (a.k.a. "Here are 10 bombs - go hit those training dummies") or kill quests ("Kill 5 Angry Rock Monsters"). I was surprised at how boring most of the quests were, actually. I would turn in "Kill 3 Trees" and get a quest "Kill 5 More Trees." Next quest zone: "Kill 5 Elder Trees." At least the combat is quick and interesting.
The tutorials need some work. The fighting/campfire/equipment/buying/selling mechanics are poorly explained. I never did discover how to craft something, even though I found lots of crafting material. And do some races better at certain classes than others? It seemed like the Barakan slayers were swinging their swords faster than my Castanic slayer. But I may have just been imagining things.
In summary: Solid MMO? Yes. Beautiful graphics, runs well, good fighting mechanics. Will it be enough to pull me away from SWTOR and the upcoming Guild Wars 2? Nope. But it's an interesting experiment, and I hope more MMOs continue to push boundaries and experiment with combat like Tera does.