For the love of gamers everywhere put a timer on achievements like this....I played 814 my first time through because I had no idea I could stop >.< Good game, though. If you have trouble try only shooting at rocks that will hit you..and only hit them enough to divert them from your gun.
I died fairly early...94 because of foolishness, but I only give this a 3...make it end or have goals or special things you get at different checkpoints or something...just going on forever makes it boring with little replay value.