Having played GH3 for a good 4 hours or so, I will give my impressions. And they'll be ordered, not a mess.
Graphics: Out of all the Guitar hero games, this game obviously has the best. The character models are nice, not edgy in anyway, and just overall nice. The downfall to the graphics are the effects/stages/ and crowd. The crowd is usually bland and doesn't move past the same animation, the arenas usually look cartoony when viewed up close and it really is just odd. The characters are now full 3D, the stages should as well. Besides that graphics are wonderfull and shouldn't dissapoint.
Gameplay: Much like all other guitar heroes, the main gameplay is the same. There are 2 big changes, the layout and the HOPO system. The layout we've all seen, and the HOPO system we've all spoken about but let me put it in my words. It definetely is much much easier. I found myself not even struggling to try to beat the solo for Cult of Personality, or Number of the beast. It just all feels so easy. But whilest I'm there, I will go out on a limb and say something else. In previous GH games when you saw a continuation of HOPO notes, it'd all go in one straight line or whatever. In this game, they like to have a few notes that are HOPO and than interrupt it with a normal note out of no where, and than continue the HOPO. Is this more realistic? I don't know, but it is somewhat of a nuisance.
The guitar: The guitar is awesome, I have to say. Just because it's wireless doesn't make it worse, it corresponds just like a wired guitar. I only complain that it can't use the rechargable pack instead of HAVING TO USE BATTERIES. It sucks, good thing I have rechargable ones. The buttons don't feel as slick as the SG ones, maybe I gotta oil 'em up or something, and occasionally the guitar won't register the notes being pressed. Not a huge deal on my guitar, but it happens.
The songs: I'll put it this way, the line-up definetely won't dissapoint. THe last 10 songs are all amazing, all the ones before that have 1 or 2 good songs in each tier. Now, here is a complaint I have about the songs. The 7th tier, 3 of the songs are almost completely chords. It's the worst case of mapping I have ever seen, because it's just ridicolous. I failed that stupid first song because it decides to have retarted notes everywhere. And than I failed the next 2 at least 2 or 3 times before beating them. Not fun, after those 3 the game goes back to goodness. I haven't beaten the damn devil yet, because it's unfair. He gets a powerup and you don't have the chance to get one as well, so it gives you a huge disadvantage. The songs are amazing though, and there ya go.
Online: Don't let anyone tell you it sucks, it's awesome. There are 2 problems I have with it though. Finding matches takes a good few seconds to even get a list of them. Most of the connections are shit, but you can still join. Now, ALOT of the matches you try to join will give you a 'game is no longer available' problem. That wouldn't bug me as much if it wouldn't have to load for the songs all over again. STUPID. And number 2, responsiveness. I was playing a battle, first to 3. I was easily taken out with a lefty flip on My name is Jonas. I returned the favor by using Lefty on Cliffs of Dover. The final song was Paint it black. Now this is what pissed me off, we were playing for a while throwing shit all around and we were both almost done. I used double notes, and an overload. I also got a whammy at that moment and knew he would be done. Now here we go, I tilted my guitar like a madman to use that whammy but it fucking wouldn't! And now he unleashes whoopass on me and I lose because the fucking whammy didn't work. That shit BETTER get fixed....
Overall: The game is awesome. Don't bitch about it, just buy it, it's fuckin sweet.