Gah... please don't advertise games based on Steam. I kinda notice this trend recently - more and more MMO games appear on Steam, and I know it's like a platform to add more people to the game, but really, every half-decent MMO has a site where you can get the info and download the game proper.
Anyways. To give some perspective here. Tera is a Korean MMO, not exactly AAA-class, but well-known and not without its merits. Game is also semi-well known for a censorship of its loli race when moving from domestic release to Europe. You can read here about it.
The cons of the game that one must be prepared for:
The game is going for something like 3 years now, so if you are a new player - there are a lot of old players and guilds who are just not interested in you. You will have to get some levels before joining anything semi-decent. That's true for all MMOs, really.
Korean style. We all know what it means, and some love it, some do not. And believe me, even though the game was censored some, I can easily say where you can get plate armor with no panties. Well, it's hit and miss really - some love that style, some hate it.
This game is not original these days. Back when it started, it was boasting quite original combat style - non-target, as it is properly called. But these days many other games can boast that. Notably - Neverwinter Online, if you are looking for free options, Wildstar, which will go ftp soon and upcoming game Black Desert Online.
Now, saying all that, the game is not bad.
First of all, it has nice variety of races (7) and classes (8 at the start of the game and 10 now with 2 classes added over the years), and the main attraction of the game - non-target combat - it does work. It's a good system, making you think not only about pressing right buttons, but also facing the right direction. Classes feel really different, ranging from heavies like berserker and lancer to fleet-footed archer.
Game provides solid content along the way. This is rarely noticed, but it should be said. A lot of games are just damn lazy and don't try to provide anything noteworthy before you get to the higher levels. Tera does okay job of having enough stuff for you. It's nothing too mind-blowing, but you will always have challenging monsters and dungeons to brave. And occasional PK if you are on PvP server, yes.
Political system. This game has it. And I can't really say much about it, cause I never really dabbled in it, but from what I gathered, player alliances can elect their own to be leaders of in-game factions which will in turn allow them to affect the state of the game world in some way. Not many games bother to do that.
So, to sum up, this is not a bad choice. Not as unique, as when this game just came out, but still holding its own. Actually, Tera was localized in Russia just this year, and from what I heard, it acquired some decent userbase there too. Main attraction of the game is still its combat system, and if you want a game where you can actually feel every hit you make - this is definitely for you. Graphics are still quite nice too, and not too demanding on your PCs.
(I still don't believe in CLs ability to play MMO games though since Spiral Knights)
PS. Also, there, do yourself a favor and use TERA online site. Information, proper forum and many download options.