I'm getting better, it does get easier if you stick at it.
I've completed everything on Easy mode, mostly with 5 stars. I'm working my way through Medium mode now and I've done about 2/3rds of the songs and managed a few 100%s but mostly get around 90-95% scores.
I can't complete many songs on Hard yet and that's probably the top difficulty I'll attempt. Expert mode is just insane. I figure the time it would need to practise songs in Expert would be better invested into improving my skills on a real guitar
I like Medium mode because it's challenging but still feels like fun and its possible to sight read songs at that speed rather than have to memorise the patterns.
Sweet Home Alabama is kind of a litmus test isn't it
I can complete it on Medium but score about 90% and in Hard and Expert mode its just nuts (have you seen the You Tube vids of how it plays in Expert mode? Sheeeesh).
Main problem I have is sometimes my Wii guitar controller starts playing without me touching it and loses me a possible 100% .... well that's my excuse anyway!
But you're right, the best part about it is the character designer .... lime green dreads and leather ftw
You any good at it then Cern? I suck even on easy mode (not really, except Sweet Home Alabama, grrr). Tried About A Girl on medium once and already couldn't follow . Tried expert to see it once and let's say I'll never manage to play on expert, that's just bloody crazy stuff. Got it for my Wii as well and it's harder than I thought it'd be 
. The rockstar designer is great though, though I spent way too much money on silly costume parts I never use and now I can't buy the Tool tour, bah. Spent way too much time with it, just ask Las about the CoH character designer and my rerolls 
.
As for WoW I'm not sure, tempted to play again, but got 6 levels to go + gear up while everyone is lvl 80 already with good gear so will be hard to find parties for heroics, etc. Got time to play now though so might do it, dunno.