Finished Defense Grid 2. Super easy/fast way to get 810 GS. Plus, it is a good game.
I didn't get 9 achievements. 8 of them are very easy multiplayer achievements and the last one which worth 100 GS you have to get a gold medal 100 times playing the same mission and the same mode. It is super easy to get but it will require 3-4 hours at least of repeating the same thing 100 times.