Er... what happened between 2 and 3?
So when I first played 3, I thought, "Boy, I hoped Neversoft really improved this! I can't wait to see what they did! Better setlist? Good online play? Better DLC?".
Thank you for crushing my dreams.
2 did a lot of things right: awesome setlist, good DLC, good engine, and HO/PO's that work. If you are a hardcore GH2 player, STAY AWAY.
The setlist is pretty bad. The Killers... AFI... St. Sebastian... Dragonforce (for most people, this is an iffy.), and a bad Sonic Youth song. Some of the charts are overcharted, AKA, more notes added, notes that make the chart iffy, and other instruments charted, which can also have extra notes. (Please... don't get me started on Through The Fire And Flames... WE CARRY ON!!!!! Sorry, couldn't resist. ;).)
As for good DLC, there is rarely any good (The recently announced Virtuoso and Dragonforce Pack, Ernten Was Wir Säen, and Def Leppard... there was one more good pack, can't remember.). Most of it is either bad or infrequent.
The engine seems to be focusing on graphics more then gameplay. Graphics are amazing for one, and it looks so smooth and nice (the drummer is still a robot kind of guy.) But there are a whole lot of recycled bad elements, like frequent bugs and glitches, and a horrible HO/PO system. Basically, if a song was at 120 BPM, and there was a green note on 1 measure, and a red another measure away, you could hold down red RIGHT after playing green... a measure later, you got the note. It can mess you up, and once you get used to it, it takes a long time adjusting back to GH2 or GH: Aerosmith.
Online play can be outright terrible sometimes. Riddled with glitches, quitters and trash talkers, and the occasinal bot/cheater, you wonder why Neversoft didn't spend more time fixing this game (more spesifically, the online play) up. Though it is good, and I can't really compare it to GH2 since... well... there is no online play in GH2.
Overall, it is bad, but has some good features (online play, some of the setlist, rare good DLC) that save this song. Neversoft... please get it right in World Tour. If you do, I might consider staying on the GH Tour Bus for a longer time.