This game is a blast, the best way I could describe it is Monaco mixed with Counter Strike and it's just as amazing as that sounds. If there was ever an early access game that deserved it's asking price, it's this one.
One thing that should be appreciated is this isn't an early access game where you'll find lots of bugs or glitches. In the many hours that I've played on all the gamemodes I have not encountered a single one, which has been pretty impressive. You will not clip into geometry, fall through the world or any other weird occurances. Everything works just as intended. The occassional lag will happen but that will occur due to the host. (Roll your mouse over the admin of the room to see their location.)
It's graphics and graphical options are very limited and it could probably run on a toaster but thats actually a great thing because that means more players will be able to play flawlessly. Personally I feel that artistic style>graphical fidelity anyday and OGAT has oodles of style. Not to mention it scales perfectly. I assume the engine is Unity, it's very well optimized.
The gameplay is fluid, responsive (if the server is decent), and well balanced. Some are quick to shout OP, but that wouldn't happen if everyone took the time to understand how to effectively use light. Light is a big part of most of the gamemodes in OGAT, it will be your friend and it will be your enemy.
The devs should truely be rewarded for their support of OGAT and the dedication to the community adding SO much to the game it's ridiculous!
Just take a look here http://ogat.gamepedia.com/GameMode
and scroll down to see all the gamemodes they are planning to add to the game! It's like they want to recreate all of the best gmod mods, and I'm all for it!
One thing that a few of my friends have made notice was that the game has no music in it what-so-ever. It really didn't occur to me at all that it would be an issue, but for some people apparently it might be. So if soley the sound of guns and grenades don't satisfy you, that might be a bit of a problem.