OKAY so the basic gist of Guy is that he LOOKS like he's a gimmicky son of a bitch with all these flips and runstops and all that
But he's not. All of his gimmicks are either unsafe, reactable(offline) or actually not that great. So over-using his gimmciks will be an exercise in frustration.
This is why Guy is a good fundamental character, because his primary gameplan once you realise the weakness of his gimmicks, is footsies, movement, counterpoking, whiff punishment, and frametrap/throw game once you get in. This requires learning how to use, and how to counter lots of basic SF4 mechanics.
I don't really feel like giving a Guy tutorial here, but he's a great character to learn fundamentals with if you focus on them. Most of the time, the solution to a problem given to you in-game is simpler than you think, and Guy is a good character to learn that with.