It's old, it's been beaten, but that doesn't mean it isn't still up there.
What really pulled me up in this is its graphics and sound, add that awesome storyline (although too scripted) and it was instantly the best game I had ever laid my hands on. The voice-acting is superb, and the weapon sounds are very accurate, and the Germans speak German! The ambiance, the soundtrack, and of course that little "ding!" when the M1 Garand runs out of ammo, they won my ears over. (Sound's even better than COD's!)
The controls were easy to get used to and to modify, which made gameplay easy for even the newest FPS player. The trouble though was the lack of movement available for the player. German soldiers and your friendly allies alike could go prone, lean on walls, shoot with just their hands peeping, and even throw back hostile grenades. You, my friend, can do nothing like that. Also, it's this annoying little ditty that every single soldier is good with his gun, and even a guy with an MP40 is as good as a sniper, and for some reason, he has the supernatural ability to hit every single shot from his SMG without being made inaccurate by the recoil of rapid fire. There IS a clipping problem in the game, but fortunately the patches had already easily fixed this. But in any case, it was still very fun.
As for graphics? Now, they're just... ugh... But for their time, they were THE graphics. Facial expressions were accurate to almost whatever situation the AI is currently in, the guns were extremely accurate, even the slightest bit of detail has been given attention, gears on soldiers, uniforms, insignias, wall decorations like paintings, posters, Nazi banners, controls in submarines are all elaborately done, each control, each dial, each lever is seen. The maps for SP missions are huge, EVERYTHING, even so much as the barrels and cans of liquid actually having volume have been given so much attention. What pulled the graphics back a little bit was the ground textures, and the edges of the maps being very obvious that they're flat, but all in all, it came through for its time.
Multiplayer is a blast! The only complaints are some of the maps being a bit too small, but everything is so cake! It's very intense, and it really gets blood pumping in your fingers. If you're sick of the scripted, linear SP gameplay, MP is gonna pull you up, definitely!
In my opinion, nothing has yet COMPLETELY overshadowed Allied Assault in the more recent titles of the MoH Franchise so far, not even the illustrious Medal of Honor Airborne.
All in all, even though it's a rather old game, and it's basically dwarfed compared to many of the games succeeding it, it'll still remain one of the biggest legends in WWII FPS.