Quake II - Awakening II
"Awakening II is a partial conversion for Quake 2 that adds 10 new weapons and 5 new powerups, replacing most of the vanilla Q2 ones to bring a fresh new feel to the game. There are also a whopping 28 new levels available to play on."
All modes apart from Assault can be played on standard Quake2 maps, so you can use the mod straight away with your favourite levels.
Full Story with some screenshots.