Normal 1 or 2-player game is easy. I recommend getting an expansion (there are more options for tweaking the game for more diffculty), or just try to start the game with more basic cards in your deck. +2 Grunts and +3 sergants in your starting deck will make the game considerably more difficult.
I was under the impression the new drone rules from the expansion would toughen it up enough to where I was losing more often than winning but i guess 1-2 player is still fairly easy. I'll play a handful more games and see how I do. If I'm still winning I'll start making adjustments.