You should check the official TERA forums, there's feedback and game-play impressions being posted there. I've been looking at it myself, I only participated in the beta for a day, but I liked what I played. It's indeed out right now, it was released today. The combat system felt very refreshing for someone who is used to only targeting and locking combat systems in other MMORPGs around. The combat in TERA is entirely dynamic, you don't even click on the mob to target it, you aim the on-screen "crosshair" and swing, fire arrows or use whatever weapon you have at specific body parts or body angles on the mob you have your crosshair on. You can AoE by moving your crosshair or of course by using skills/talents that will do the job automatically.
For example as a warrior (Berserker, focusing on dps) there's a skill similar to a whirldwind 360º spin, you don't have to do it yourself with the mouse and the crosshair. But you can also use your "basic" melee attacks (of course taking an example for melee classes) and move your mouse/crosshair around as the character does the melee animations to hit different mobs around you. The first swing you point at one mob, then you time up the animation for the second swing to hit another mob behind you by moving the mouse (or camera, or crosshair, if you prefer) and you do "slower" AoE that way as well, rather than having to turn the camera to face mobs and lock on them one by one.
It's what I like the most from what I played, the combat. That alone nearly convinced me to go for a subscription plan of six months. I'm resisting the temptation right now though, I have Diablo 3 to buy in two weeks, and I'm considering to pre-order Guild Wars 2 as well. For now, until June 1st, you save some cash (20%, 30%, etc) by subscribing and activating a monthly fee plan of your choice starting at 3 months, then 6 months, etc. In my opinion TERA is worth a try (say... for a month at least). If you buy the game you have a free month (30 days) access to play, after which your subscription monthly fee plan kicks in. If I had no other interesting games to play, I would buy it and at least let that free month of access do its job to give me a solid impression on most of the game's content and features.
In my case however I have plenty to play and I must cool down the hype which playing the beta for a day created. I would recommend also watching recently uploaded and HD footage of the latest version (final release) on YouTube, check for videos no older than maybe a month, otherwise you'll watch outdated features, or quests or content, etc.