Smash Hits takes 48 songs from past Guitar Hero games (everything from GH 1 to GH: Aerosmith) and upgrades them to work with the full band experience introduced in World Tour. All are master tracks, so I'm sure licensing issues had some impact on the final list, but a quick look at the list won't inspire much excitement. There are a number of top-notch groups like Foo Fighters, Aerosmith and Nirvana, but even then some of the track selections are odd ("Back in the Saddle"? Really?) The good news is that the songs are a lot of fun to play with a group - so there are some redeeming factors.
The visual style is similar to past games. Beenox, who took over development for Smash Hits, does a good enough job at keeping the status quo. Everything is more inline with World Tour than GH: Metallica, so the gritty "realism" isn't as prevalent in the style. Granted, you won't notice most of this while playing, so there's nothing to get worked up about.