What is it? Russell Crowe stars as Maximus, a Roman general under Marcus Aurelius turned slave under Commodus, turned gladiator turned folk hero. Ridley Scott directs and single-handedly resurrects the dead-and-buried sword-and-sandal genre.
Why did it win? See above. The other nominees were: Crouching Tiger, Hidden Dragon and Traffic (both a bit too foreign), Chocolat (not safe for diabetics, and many older voters may suffer from that) and Erin Brockovich (female in the lead role? It was never going to win!).
Did it deserve to win? Hey, we're not going to argue with Crowe's Maximus - have you seen that guy? Dude be angry! The fact is that this is as Oscar-y as it gets - epic, vaguely historical, glorious looking, huge in both scale and emotion - and to say that there were better films that year is more or less moot. Also, Gladiator is a big film with a smart script and a great cast, so it's hard to dislike.
Worth a look? Hell yes. Marvel as a star is born, and memorize Maximus' mannerisms to use in your next office meeting.