Well I downloaded your game, it's 12 to 15 fps on my athlon 1800xp 256DDR geforce2 mx400 and that's frightfully slow.
I think maybe you should at least include an option to remove the background (trees etc..) cos they don't really add much except processor overhead just the pipes and the music are cool. Even if you get the fps up he could turn a bit faster so you can have a check for the monsters and get more involved in the game.
Cool Idea though, real simple yet effective.
ZX Spectrum 48k Issue 3, Radio shack Tape drive, Rank arena 12" T.V. set.