The absolutely free 4-player co-op from Valve, entitled Alien Swarm, also offers first person shooter gameplay, if the player so desires. Using simple console commands (listed below), a player can switch from a top-down view of the arena, to a first-person view.
While the option is great, it is probably only fun as a novelty, as several players have complained at the how ridiculously hard to control the game becomes, when one can’t keep track of the rest of your team from an aerial perspective. Skilled squad-based FPS players will possibly not find this too difficult, but other complaints include reduced graphics and lack of hacking screen operability. Do try your hand at it though, and tell us what you think! Check out the console commands below, and, an automated script version, benevolently provided by a Slashdot member. Also check out a video of it in action.
alias "povtoggle" "normalcam"
alias "normalcam" "asw_hide_marine 0; asw_controls 1; thirdperson; alias povtoggle fpscam"
alias "fpscam" "asw_hide_marine 1; firstperson; asw_controls 0; alias povtoggle normalcam"
bind "p" "povtoggle"