I remember an old mod I made back in v0002 (rtb 1.045).
It was EXTREMELY basic, however people seemed to have fun in it.
I can't remember what map it played in, green hills or something, forget.
But this is how it went:
Red vs Blue
You have a big block which you spawn near, and you need to defend it.
You had two weapons, a cool looking sword/blade I modeled (and lost, wasn't flat shaded anyways), and a wrench for repairing.
The giant block had I forget how much health.
My favorite part was that I used that 'cellshading' method by making an inverted black block around a normal colored block above the giant block to represent the block's health.
Very basic, but still fun.