Grand Theft Auto IV: The Ballad of Gay Tony will allow for 250 more gamerscore points to obtain. After scanning over the list I couldn't any story releated spoilers, so feel free to check out the list that details a few of the episode's new mini-games. Check it out!
TBoGT: Gone Down - 5 
Complete all base jumps. (The Ballad of Gay Tony)
TBoGT: Diamonds Forever - 5
Complete the Trinity. (The Ballad of Gay Tony)
TBoGT: Four Play - 10
Hit a flag with a golf ball four times. (The Ballad of Gay Tony)
TBoGT: Bear Fight - 15
Win the L.C. Cage Fighters championship. (The Ballad of Gay Tony)
TBoGT: Catch the Bus - 15
Dance perfectly in both Tony's nightclubs. (The Ballad of Gay Tony)
TBoGT: Snow Queen - 20
Complete 25 drug wars. (The Ballad of Gay Tony)
TBoGT: Adrenaline Junkie - 25
Freefall for the longest possible time. (The Ballad of Gay Tony)
TBoGT: Maestro - 30
Finish the Ballad. (The Ballad of Gay Tony)
TBoGT: Past the Velvet Rope - 45
Score 80% or above in all missions. (The Ballad of Gay Tony)
TBoGT: Gold Star - 80
Score 100% in all missions. (The Ballad of Gay Tony)
Source-Xbox 360 Achievements.org
