Hm, I like the basic idea, but it would be even cooler imo if instead of monsters you were attacked by regular bots (or human players of course...).
But wait, there's more...
In the base, which could be a castle, bunker or other large building, there are several respawn devices. If the attackers manage to destroy them all the match turns into last man standing for the defending team. When the last one dies it's game over for them, and the attackers have won.
BUT, the attackers also have respawn devices, namely special vehicles! These too can be destroyed, and the attacking team subsequently wiped out.
Simply put, the objective of this gametype is to totally annihilate the enemy team, kill them all and make sure they stay dead.
As an added twist you can also capture and use enemy respawn machines, so even if you lose yours there's still some hope, you could still ultimately win the match.
You could also have 2 fixed bases, like in ONS or CTF, but perhaps the 1st version (vehicles vs base) would be more dynamic and interesting, like a real medieval siege only wih high tech equipment.
