Wake Island from Battlefield 1942.
It's a small island in the shape of a "U" that allowed essentially every play style imaginable:
- 1v1 and/or large scale gunfights
- dogfighting
- fighting on the sea (complete with cannons that could attack ships, and boats to board ships/reach the island)
- cover in the form of foliage, houses, and vehicles
- enough space to use ground vehicles, including tanks and jeeps
- a small enough map that you could drive from one end to the other in a couple minutes, meaning you were never far away from the action
- the shape of the map allowed you to swim across from one point to another to try and capture a point
- hilly terrain, allowing you to sneak past enemies on either side of the island
- guard towers for sniping, that also acted as choke points for people trying to run/drive into capture points (see image above)
It's seriously the best ever. Don't know how well it'd translate into modern games, but I spent days camping out as an engineer on Wake trying to surprise people with TNT.