Two extremely easy games for 1000 GS are COD2 and COD:MW2. Both require almost no skill. Borderlands is another one, although to complete the game, you have to download a bunch of DLC. If you've got lots of time, you can get 1000 in Skyrim without too much trouble. It's also pretty simple to get a majority of the GS in one playthrough of the following games: Bioshock, Assassin's Creed 1&2, Dead Space, Saints Row 1,2, & 3.
It depends on if you're a completionist. But there are many other games out there that you can get 700+ points on in a single play through without having to kill yourself to do it. That is, if you care about GS.
The Darkness 2, seriously this is a really enjoyable game to play through, alone or with friends as there is 4 player co-op available. Don't worry though, if you prefer flying solo all of the achievements can be obtained by playing the single player and playing through the multiplayer on your own.
Honestly, I had so much ripping people in half and laughing pretty hard at what passes for an Italian accent in that game I didn't even realise I was getting so many achievements, plus with mission select it's physically impossible to miss an achievement.
Once you get past the trading / co-op partner achievements Fable 2 and 3 are pretty easy, Dead Island you get about 95% of them pretty easily too, just the completing act 1 and 15 waves of the arena mode with each character that can be a pain.
The list of games that I have done myself, for friends or are sitting in my draw waiting to be finished;
CSI - Deadly Intent CSI - Fatal conspiracy Madden NFL 08 Smackdown vs Raw 2009 Smackdown vs Raw 2008 (Friend needed for online achievements) Prey Halo reach (If you can do previous halo games this wasn't hard at all and was a lot of fun) Gun Sherlock holmes vs Jack the ripper Quantum of Solace EA sports FN 3 Tinker (It's also free on games for windows live) Assassins creed 1 Torchlight (arcade game) Battle LA (arcade game) Kung fu panda Iron man Portal: Still alive D&D daggerdale After burner climax Saints row the third Iron man 2 Fable 3 Modern warfare 3 Modern warfare 2 Dead rising 2: case zero (arcade game) Fable 2 Brink Cameron's Avatar Saints row 2 You're in the movies Force unleashed 2 Lego batman X men origins Wolverine Operation flashpoint red river Battlefield 1943 (arcade game) Dead space Fifa 06 RTFWC Harms way Borderlands Medal of honor Phantasy star universe (easy but long) Wanted: Weapons of fate DTR: Retribution Oblivion Clive Barker's Jericho Fallout 3 (PC) WWE Legends NBA 2K6 TMNT Lost via domus Assassins creed 2 The Bourne Conspiracy The godfather 2 NFS Most wanted Dirt CSI - Hard evidence Eragon Madden NFL 06 Harry Potter OOTP Terminator salvation NFS Undercover Dark sector Brothers in Arms: HH Avatar TLA: TBE Jumper Dash of destruction American wasteland Amped 3 Lego star wars 2 Lego Indiana Jones King Kong The simpsons game Guitar hero 5 Band hero The Spiderwick Chronicles
Plenty of easy games, that's just the list that I've played, if you're in the US there are a lot of games available there that aren't available to EU and Japan that are really simple. If this thread keeps growing I'll keep my list updated.
The second assassin creed is quite easy to 1000 gamerscore, though finding the feathers may take a while. The others are nearly as easy if it weren't for the 100G one for getting full synchronisation on the every thing. Also both Oblivion and Skyrim are easy but time consuming (especially level 50 on Skyrim).
If you're using guides and what not to find everything, you can get probably get 80% of Dante's Inferno's achievements. A lot of them just come from playing the game to completion. The only downside is having to play through the game again on a new game + to max out both skill trees. Also, do Gates of Hell on the easiest difficulty to get that done and out of the way fast. Honestly wasn't that hard, since there are no difficulty based achievements.
I didn't see the legendary one mentioned: Avatar, the Last Airbender. 1000 GS in about 5 minutes... LOL! Realistically, I'm not a great gamer, so for me to get 100% GS in Assassin's Creed II, Borderlands, and Maw, you know those are easy. I'm 5 away in Skyrim, that one is easy as well. Fallout 3 took some time, but again, knock the slider down to a difficulty you can handle, and pay attention to the missable achievements (just a few) and it's no problem to get 100% on one playthrough. I'm wanting to finish 100% in Portal 2. Just need to find a co-op partner to get the last few difficult ones...