Here we have some recommended DOOM2 MODS, playable even with the FreeDOOM WAD:
(Download the complete IWAD and use it with PrBOOM for example)

For example on the command on Linux for STRAIN.WAD, if you have the file among with the other freedoom.wad one: 

prboom -game freedoom.wad -file STRAIN.WAD.

If the game has a DEH file, well, the sintax w/ prboom is:

prboom -game /path/to/freedom.wad -file game.wad -deh game.deh

Yep, all mods should run fine on prboom+freedoom.wad for Mint PPC, which I am tweaking a bit for ex-PowerMac OSX users which did the switch to Linux Mint PPC and want to play some old games. Marathon is available too :) .

http://www.nongnu.org/freedoom/download.html

Batman (Lovely and gothic gameplay)

http://www.doomwadstation.com/main/tc.html#BATMAN

Quake II (Not bad. for the doom engine).

http://www.doomwadstation.com/main/tc.html#quake2

Strain

http://www.doomwadstation.com/main/tc.html#STRAIN

Blood (Not so awesome as the original BLOOD for DOS, but it's
a great aproximation)

http://www.doomwadstation.com/main/tc.html#blood

Fistful of dollars 

http://www.doomwadstation.com/main/fistful.html#

GoldenEye (Agent 007 at your service)

http://www.doomwadstation.com/main/tc.html#GoldenEye

Zombies (Romero would be proud)

http://www.doomwadstation.com/main/zombies.html

HACKX (Awesome TC, it looks like a new game)

http://www.doomwadstation.com/hacx/hacx.html#

Aliens (Great for multiplayer matches)

http://www.doomwadstation.com/main/aliens.html#

Dr Who (Exterminate, exterminate)

http://www.doomwadstation.com/main/drwho/#

Mortal Kombat (You will get a FATALITY if you don't play this)

http://www.doomwadstation.com/main/mk.html

DrDooM, Goblin, and others

http://www.doomwadstation.com/jeremy/tcs.htm#

Quake 

http://www.doomwadstation.com/quakedoom/#