You'll have to deal with a clunky interface and menu, silly single-player missions, brain-dead A.I., bizarre vehicle physics, horrible net code, dull graphics and sound, and more bugs than a Georgia swamp in June
This and many of the other reviews make it sound like at the time it was released it was a buggy mess. Reviewers said that the single player was worthless (you don't say), and that the multiplayer net code was so bad that players and vehicles would warp all the time. Maybe this has improved with patches over the last ten years.
At the time there was a backlash against publishers that would ship games early that were full of bugs. Many reviewers would only review based on the initial release version in response, to get the publishers to stop releasing games early and treating paying customers like beta testers. It sounds like if the game is so much fun to play, it may have fallen victim to the publisher's decision to release it before it was ready.