Well, the throes of boredom and frustration have again hit me. 
 
After upgrading to a 360S yesterday and discovering that my licence and data transfer destroyed half of my Forza 3 garage (with particulars to VIP and unique one-off cars), I've realized that I need a new 360 game. 
 
My current list, in order of  frequency of play, parentheses describe how each is played if relevant:
Final Fantasy XIII (Mission cleanup, otherwise done)
Modern Warfare 2 (Only when playing with friends, fully beaten) 
Forza Motorsport 3 (Done, as far as I care) 
Tales of Vesperia (On loan to a friend, only extra dungeon remains) 
Bayonetta (Done, as far as my skill allows)
SoulCalibur IV (Local Multiplayer only, fully beaten) 
Forza Motorsport 2 (Fully beaten)
PGR 4  (Fully beaten)
Call of Duty 4: Modern Warfare (Fully beaten)
Burnout Paradise 
Mirror's Edge (Done, as far as my skill allows) 
Orange Box (Fully beaten) 
Lost Odyssey (Fully beaten) 
Left 4 Dead (Fully beaten) 
Halo 2 (Local multiplayer only) 
Halo 3 (Done, as far as I care)
 
I have a strong preference towards racing games (with preference towards simulation ones), RPGs (with preference towards Japanese ones) and FPSs.
 
Do not recommend the following, as I own them on PC: 
Mass Effect
Mass Effect 2
Dragon Age: Origins and Awakening
TES3: Morrowind 
TES4: Oblivion  
Fallout 3 
Devil May Cry 4 
Bioshock 
Bioshock 2
Anything Codemasters Racing
Anything Valve 
 
Thanks for your help!