I've been playing guitar for 12 years and when I got Guitar Hero 3 I beat it on hard 5 hours after I purchased it because the dexterity of my fingers was greatly increased from 12 years of guitar. You just have to get used to the eye hand coordination.
Another vote for the sucking at guitar hero, im alright at guitar tho. Its ridiculous, a drunk girl who cant play a real guitar to save my life challenged me to a game, of course I accepted being sober I thought it would be a walk over but i got slayed! couldnt believe it! Maybe its a general consensus that guitar hero is best on drugs (in general)