I haven't seen the mention of bots (which are pretty awesome) but splitscreen multiplayer online is already a seller for me. Finally a fully fledged, yet simple FPS I can play together with my friends.
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Anyone remember Turok Rage Wars? I think this game will funtion similarly. Basically there's 4 slots for players. For any sot that isn't filled, a bot takes the place. So with Protocol, I'd imagine it will focus on keeping 8 active characters running in the matches be it players or bots.