I ran across the site for Battleswarm, today. Take a look at this description from their "About" page that explains how the game works.
"This genre-busting new game pits players of First-Person Shooters against players of Real-Time Strategy in epic online battles waged between elite Human soldiers and massive swarms of alien Bugs. Each player on the Human side takes control of a single soldier in first-person mode, armed with an arsenal of high-tech weapons and armor. Players on the Bug side see combat like an RTS, building hives, breeding bug units, and sending them into battle. This unique contrast of genres provides revolutionary gameplay on both sides.
Enemies in First-Person Shooters used to come in only two types. If you wanted to fight large-scale armies, you had to play against AI. If you wanted to fight other players, you had to fight small squads of evenly matched soldiers. Now Battleswarm provides a new third option: the player-controlled monster horde. For the first time in an FPS, you fight an alien army that is controlled by real intelligence. No longer must you settle for rigid and unrealistic AI. You’ll need every weapon at your disposal to out-fight a Bug army that uses large-scale strategies to exploit your weaknesses and attack from where you least expect it.
As a player on the Bug side, you’ll enjoy a whole new dimension added to the standard RTS. Whereas most normal games feature strong “hero” units with special abilities, no hero in any RTS is as versatile as an FPS player with an arsenal of guns, grenades, and high explosives. But have no fear! You’ve got a wide variety of deadly Bug breeds at your disposal, plus the hives to create more. With an entire army at your disposal, it’s your job to outflank and overwhelm your heavily-armed Human enemies.
Better than two games in one, Battleswarm combines an FPS like no other with an RTS like no other to create a new game genre: the Combat Strategy. Whether you crave the nonstop action of the Human side or the cold and calculating strategy of the Bug side, you’re in for a gaming experience never seen before."
It looks pretty interesting! I haven't delved too far into the site, yet, so I'm not sure exactly how massively multiplayer it is. I don't know if it's a giant, persistent world or if there are lobbies with a limited number of players who can join. Either way, it looks like it could be fun.http://www.battleswarm.net/game/