TERA is another free to play MMORPG like many others. There isn't much separating it from the rest of them and it feels a bit bland and boring in many ways. I've spent some time with it and didn't completely hate my time, but I also wasn't chomping at the proverbial bits to play more of it and switched to another game when the opportunity presented itself.
Let's forget the weirdly sexualized everything - and the race of literal children - and concentrate on actual gameplay and systems. TERA boasts active combat - unlike other MMOs where you push buttons and stuff happens regardless and while it's not false that the combat is a bit more active than, let's say World of Warcraft - and I feel that WildStar did more or less the same thing - pushing a button to fire a spell in a straight line isn't much different than pushing a button to cast a spell automatically at your target. I'll give it one thing; being able to dodge attacks by moving away really helps - but maybe too much, since for the 18 hours I've played the game, I didn't die once. I also never had to use a single health potion.
One thing that hinders their 'active' combat a bit is the move chaining system. The game will create chains of skills for you - and you can create them as well - that are usable by pressing the SPACE key. For instance, a skill that makes you dodge and reload might be chained with a powerful shot with a cooldown, followed by a big projectile, followed by another reloading skill, then the powerful shot again. It's a neat trick, but what's the point of having two bars full of skill hotkeys if you could just mash space and get away with it? To expand on that problem, what's the point of having all of these skills? You're probably going to only use a few ones and ignore the rest, especially if they get bound to the F keys, very close to irrelevance. But you can customize your skills a little by using Glyph Points to add new effects to your powers.
Another big issue I had with the game is terrible pacing and quest placement. This was caused by bonus experience given out like candy. +100% because of an event, +50% by using an item, +100% with the free Elite Status the game gives you - to show how cool you can be by paying real money - and so I've just out-leveled everything I ever tried to fight. I feel that questlines were broken because I couldn't stand fighting stuff that just died to auto-attacks forever and I moved on to other maps where I had even less quests to do. The quests are typical MMO fare, with some weird escort missions where a guy will walk around super slowly while aggroing everything in sight, and while the game is kinda good at showing you on the world map where your objectives are, it suffers from having you move all across the world to talk to NPCs as part of quest lines. Going back to the capital for the Nth time to talk to some guy isn't exciting, nor fun, nor should you have to do that more than once.
Finally there's the issue of gear, where TERA fails into the bland soup of MMO gear where you never feel that your better gear is actually doing anything over the old one. In a game where you can't die - mainly from being overleveled, in part because you can just dodge out of anything - finding better stuff with a bunch of abilities and numbers and purple text feels hollow. No matter if you tell me that my new gun is 'superior' and does a bunch of things, if I can kill everything very quickly without a problem, how will I be able to judge that? Same thing with armor, and everything else, you're just watching numbers go up.
TERA isn't bad, it's just bland and boring. If you're on a quest to try all the free to play MMOs, be my guest and try it out, otherwise you can probably safely move along.