'aight. I think I'll redo the engine I posted from start with all the tricks I've learnt since then, and I'll not code the useless stuff. (Like the stealth. They won't gun for you if they can't see you, but firing a gun won't draw them like iron filings to a super-magnet, and you can't "hide" from them by putting the gun away when they can't see you.)
I'm thinking TDS, with different stats for each playable character. (so if you play as bill, you have regular health and 2x fire rate by default, and if you play as bob, you have 1/4 health, but you do 4x damage; and stuff like that.)

I can also do vehicles, although that's a little borky, and wee might want to avoid having scenarios where you can drive a car and run on foot in the same "room", if you know what I mean.  So, seperate driving levels and on-foot levels. (if wee have vehicles at all, of course.)

Anywho, time ticks, and I really should get a decent night's worth of sleep; energy drinks won't keep me above water forever.