First off, I'd like to say that this isn't going to be a particularly detailed review.
Second, this review assumes you've already made yourself somewhat acquainted with the game by watching youtube videos or some such.
Global Agenda is a futuristic FPS MMO with a few RPG elements. There's PVE missions (think Borderlands) and a "virtual reality" PVP Arena (think TF2, or Tribes). Obviously the majority of the focus is on PVP and that's what I've played the most, so I'm focusing on that.
Before we even get into gameplay mechanics, I want to note that this game runs HORRIBLY. Whether it will run well or not on your computer is really a roll of the dice, even if you have all the recommended requirements. On my gaming laptop I get an average of 25 FPS when nothing's going on, and it can get as low as 5 FPS when there's a lot of enemies on screen (which happens often in PVP due to the game modes)
Now, on to the gameplay. There are several game modes, and all but two of them focus on capturing and holding Control Points, much like in TF2. Also a copy of TF2, the game's Payload mode has you escorting a bomb to a destination along a guided path. The only "unique" mode is Demolition, which has you taking a Mech to the enemy's base and self-destructing it.
They're all fun enough, especially if you're on the winning team. But this game has some serious flaws. For one, the four classes in the game are not balanced at all. I won't go into details, but just know that the game has poor balancing. The other problem is that the game throws low level players in with players 10 and 20 levels higher than them with far better gear and more skill points AND more game experience.
It's a good enough game, but it's flawed in too many ways. I could forgive the lack of class balancing, I could forgive the lack of tiered gameplay to keep high level players away from low level ones, and I could probably even forgive the terribel frame rate issues if it was the ONLY problem with the game. It's not, though.
If you haven't played Global Agenda and want to know what it's like, picture a combination of Tribes and TF2 and then throw in terrible class balancing and horrible frame rate issues and you just about have it.
I score this game an arbitrary 67/143