A good story-driven FPS with lackluster indoor level designs that holds it back!
Another thing that Halo does very well is adding different kinds of vehicles that all will serve their purpose during the course of the game. Once you get used to the loose controls you'll be just fine... remember this ain't a driving simulator. The enemies you'll face do lack in variation until the Flood comes into play, but the excellent AI will make the fire fights refreshing every time. The AI of the marines that tag along once in a while is also excellent.
The graphics are very good considering this is a 2003 PC port of a 2001 XBOX game. The thing that holds the game back is the indoor level designs. Certain sections of a particular level are copy/pasted to a great degree. A lot of the times I was wondering if I was going in circles (The Library level). If the game didn't have an excellent story and great combat, I would of quit the game (probably in the middle of the Library level). To the contrary, the outdoor levels are nice.
In retrospect :
THE GOOD
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Great Combat and Weapons - Drivable Vehicles are great - Excellent story - Outdoor levels are great - Good AI - A great Port
THE BAD
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Bad indoor level design - Not much variety in enemies until later stages - Music is not memorable