I've been having a lot of fun in Battlefield 1943 on Xbox Live. I'll post a full review soon, perhaps tomorrow, but I want to point out one feature in particular which I'd like to see in more FPS games.
1943 makes great use of elevation. Half or more of each map isn't flat. As a result, players are constantly using hill slopes and water banks as cover. The maps are almost entirely exterior, but players are still constantly surprised by enemies coming up from behind, below, or above them... or even right in front of them (hidden by a slope).
Elevation plays a strategic role in anti-tank combat, since tanks are vulnerable to explosives on top, just behind the cannon. A tank can drive onto some raised areas, but then its guns are useless as they cannot aim down.
Elevation also provides for some unique experiences. I once drove a tank up a slope that was barely wide enough for it. Below the end of the incline was a hill checkpoint, particularly hard to capture. Players are used to infantry attacking from the incline I was using, but not used to seeing tanks there. I kept driving forward and dropped my tank on top of an enemy, crushing him. Another unique experience is hearing a plane but not seeing it until it appears from behind a hill and drops its bombs on you.
I'm sure even more could be accomplished when elevation is considered an explicit game feature.