Talk about your favorite video game modifications. For me, my favorite mod is Black Mesa.
The Shrek tank for Left 4 Dead 2.
The Avatar: The Last Airbender Mod for Civ V.
Empires, a standard RTS but with player units instead of bots.
The RTS side of the game is much more engaging with other players feeding back their progress, or arguing against certain orders and generally managing themselves.
The FPS side is a unique, changing battlefield where both teams are in a battle to adapt to their enemy and control the map.
I'd say Sourceforts but it has been dead for a long time ;_;
Frostfall, for Skyrim.
I haven't played Skyrim with mods yet, but from what I've seen from a Skyrim LP, Frostfall really looks like it will be my favourite game mod of all time.
Jedi of Skyrim: KotOR system, with the Revan and Starkiller armor mod.
Because I like being Revan. xD
Alternately, XCOM: Long War mod. I haven't played it yet, want to get used to the Enemy Within changes before I throw more at it, but I am looking forward to having a larger, more customizable squad!
And then naming them all after my favorite characters.
Which will backfire horribly.
But, but, but Starkiller...
And Starkiller, yes.
It's the Sith Stalker armor, for those interested.
Playing a sith is always fun! xD
Starkiller is a Jedi not a Sith now.