Do you have a toy guitar (as in a Rock Band or Guitar Hero one)? Because it's more of one of those types of games.
You can play it with a keyboard if you must though, but I feel like you're not getting the most out of it. I posted a video of me doing the first level on Extreme difficulty with a keyboard.
It's a decent game, but it's more of a game that would be fun in a social setting, where you can laugh at your friends failing / spazzing out trying to hit the right notes.
Meh. I don't have a guitar. Thanks for the impressions though. Definitely rather find that out before it's added to the library.