The problem now is that HALO is old news so to speak, it came out almost 2 years ago. Had it been released when it was supposed to be on PC it would have undoubtedly skyrocketed to hights unknown as a groundbreaking shooter. But by now, its already been beaten to death. But enough waxing on about it... lets get down to business.
The grahpics in HALO are still impressive. Character detail is pretty damn good, and there is nothing like jumping in a Warthog and ripping through the terrain. The biggest drawback to the graphics is that they don't appear to change a whole lot as you play through the game. There are 3 primary environments that you find yourself in. You have your Outdoor (daytime) action, Outdoor (nighttime) action, and then the Indoor areas. You might consider a fourth to be the Snow areas, but thats kind of a stretch. The absence of really versitile environments is not really a platform specific problem, afterall it has been that way from the beginning.
Gameplay is strong, the single player campaign has a wide variety of difficulty levels that you can choose from depending on your skill and how much you want to work at plowing down the hoards of enemies to reach your goal. The AI is pretty good from what I have seen. Friendlies will make a serious effort to help eachother out and if you are in a vehicle and there is room, they will jump on board and man gunner positions as you try to run down enemies on your way to your destination. The Covenant make use of a wide variety of weapons and tactics to thwart your advance. They will take cover behind rocks and trees and will try to flank whenever possible, so eyes in the back of your head is a must. The vehicles really do add quite a bit to the game as well. The Warthog and the Banshee are my personal favorites. They combine excellent manuverability with adequate firepower.
Throughout the game you can pickup weapons from fallen friendlies and enemies. You are limited (still) to 2 weapons at any given time. So if you pickup an alien weapon it will auto drop your machine gun, or pistol depending on the weapontype you pickup. This deffinitely makes you keep track of your ammo and weapon status. It also encourages a serious hunt through the battlefield after a large firefight to find more ammo or new weapons before proceeding on to the next area.
All things considered, HALO remains a good title for fans of the Sci-Fi/FPS style. The use of vehicles and game modes for MP is fun, providing you can find a server that can handle the load, and you have a PC that can do the same. It's a shame that it took 2 extra years to move Halo from the X-Box to the PC. Hopefully this will not remain an ongoing problem for GOOD games transitioning across platforms from the X-Box.