Battlefield 1942 is a fantastic game, but it cannot stand up to Battlefield 2 or newer titles in the series.
The game play is great, and original, which makes it a good buy, because of it's value, which makes it very cheap. You can pick it up now for $20 (Australian) and even cheaper on Ebay. The game play consists of tank combat, infantry combat, air combat, and combat in general. You can fly historically-accurate WW2 aircraft, which do roles from fighter, bomber, dive bomber and torpedo bomber, in all types of battles.
Air combat is fun and great, but if you are on the ground, the air power can become annoying, as a single plane, can take you out, when you have just spent 5 minutes walking across the map at Market Garden, to capture that flag, and you have no defense against them (except for cover (if you can find it) and AA (if you can find one.) Ground combat is no so messed up. Although there is a order (assaults and medics own close-up, snipers own anything but close-up, anti-tanks suck for everything but anti-tank) which can be kind of annoying if you find yourself getting raped by sniper campers, or if someone leaves explosives all over the place, but the community is quite good, and that sort of stuff is uncommon. Tanks own everything, but AT is there to balance that.
Naval combat is annoying, as you hardly ever get a ship, but when you get one, it is a blast, and dueling other ships is also a great waste of time. The graphics and the sound are 2001 quality, so buy this game for the great gameplay, not for the graphics and sound. That said, the graphics do not downright suck, but they are not up to 2007 standards, so if you want good graphics, get a newer Battlefield. The game, as I said is good value, and for $20 ($50 for all expansions) it is a great buy, if you want something to hold you over to the next great next-gen title that is out. It will last you a while, like a year on-off.
Battlefield 1942 was great in 2001, and now it is still good, but the graphics, and the sound spoil one of the best WW2 FPS's around. Let's hope that EA does a DX10 remake.