I haven't read the whole thread (but will shortly), but the Quake series has excelled as a multiplayer series primarily in the odd numbers. The 1st and the 3rd. Yeah I know people played Quake 2 multiplayer, but for purity, it just wasn't full of win like Quake 1. Nothing can beat that speed. Then of course Quake 3 Arena was entirely MP.
The even-numbered series was always the most plot-driven story-based SP experiences. I played Quake 4 SP, thought it was excellent. I don't think I've even tried multiplayer.