Heh, I've got a pretty good handle on it, actually.
I'm working on a strategy mod, in which the players control a squad of 3 grunts. It's shaping up to be pretty cool. Pretty much all I've got left to do is playtest it, so it should be finished in a couple of weeks.
It's set in modern times. The player controls a squad of grunts, the same kind that you fight in the normal game. You get one with MP5/grenade launcher, one with MP5/hand grenades, and one with a shotgun.
I'm the only person working on it, so I can't make alot of custom stuff like models. But I have made some new maps for it.
Well uh... the players don't get to do any fighting themselves, they're like disembodied ghosts that control the troops. So it basically plays like a classic strategy game. A player 'dies' when the three grunts in his squad are killed. A frag is awarded every time one player's grunt takes out another player's. An additional frag is awarded if it was the last grunt on that player's squad.
It works for deathmatch and it has rudimentary teamplay support. I'm also working on a round-based "Last Man Standing" game mode.
I'm interested in making mods for Half-Life yet the only editor I have is gmax... and that's quite confusing... are you using any editor programs if any?