If you'd like, feel free to add Reaiming as I'm sure I could help you get some achievements.
Easy games to boost gamerscore:
Halo: Combat Evolved Anniversary
Halo 3 ( Favorite game )
Halo Wars
Halo Reach
Halo 4
Skyrim
Gears of War 3
Gears of War Judgement
Call of Duty 4
Call of Duty Modern Warfare 2
Call of Duty Modern Warfare 3
Call of Duty Black Ops
Dead Island
Oblivion
King Kong ( Horrible game, easy GS )
I space the Bioshock series purely for it being one of my top 3 favorite series, keep in mind I've been a gamer for around 10 years.
The games are extremely easy to get achievements in, but are really fun games to play!
Bioshock
Bioshock 2
Bioshock Infinite
- If you are interested in a longer list, feel free to PM me and I'll form a longer list of games that are easy to obtain gamer score in.
I hope my post helps!