I am one of the few people who have never played one of the Halo games before. Mainly because I refuse to buy an Xbox, so all I knew about this game was the name tag that gets tons of hype. Granted I knew that this isn't the normal genre that Halo is best known for.
In this game you control a single soldier, you can carry two weapons and have various special abilities. I only found out about these until the last 2 chapters however. While the game is fairly short, and there is hardly any story line to it, the gameplay is somewhat addictive. I found myself being able to finish the game in one sitting. The individual levels vary between 2 minutes and 10 minutes long. The game is very fast paced and it doesn't give you chance to get bored.
Towards the end of the game, I found my self being very overpowered due to the fact that I had hoarded experience points (because I didn't know how to spend them) and could use the homing explosive drone on each of the final levels, which kind of made the whole ordeal very easy and probably ruined the experience a tad.
The enemy units are all very samey, throughout the game, varying from the regular grunts who just keep pouring into you, to your beefed up melee combat commanders who will kill you in one shot.
The controls are fairly simple. Move around with WASD and aim with the mouse. The vehicle controls on the other hand left me driving into walls without knowing which way to turn around for a few seconds each time, left me very confused.
You can't ask much more of this sort of game in terms of graphics, it's a very regular decent graphics top down shooter. Nothing more, nothing less. Yes there are prettier games out there, but my gosh there are plenty worse.
All in all, I'd say pick this game up on the cheap, or if you are a fan of the Halo universe, you may get a kick out of it more than anyone.