I'm working my way through GH3 right now.
I'm almost done with a Hard Career. It's a ton of fun and not as hard as it looks. Some of the more dificult songs, like the kid in the video, just require memorization of the patterns, but that's the same for playing real guitar anyway.
They have a practice mode where you can slow the song way down to like 1/4 normal speed.
When you get aggravated with it, you just need to take a break and do something else fo awhile. Heck, i used to throw real guitars across the room.
