Visually, Decades suffers from the same problems that Guitar Hero 2: Encore had; mainly the developers used the exact same engine without any sort of refinement. The character models are the same as they were in the previous DS Guitar Hero, but now they have different outfits which don't have any effect on the core gameplay other than to say you have the super expensive outfit. Honestly, I didn't use any of the outfits that required a purchase.
This time around, the story sets up a music festival that you are touring with and there are different areas of the festival that you must play. The theme of Guitar Hero On Tour: Decades is music throughout different decades so each stage has its own visual theme. The different decades include Modern, 2000's, 90's, 80's, and the 70's and you see some pretty typical stuff for each area. The 70's stage has flowers and psychedelics and the 80's use lots of neon colors and day glow.
Guitar Hero On Tour: Decades manages to successfully utilize the DS's audio abilities. Each of the songs sounds clear and crisp through the system's speakers, but it would really be better to use headphones. Headphones are better so you can stay more focused on the rhythm and timing and also so you won't annoy anyone else in the room with a questionable song choice.
There are around 35 songs to play and unlock, and while the last three song tiers (70's, 80's, and 90's) are somewhat enjoyable, the first 8 songs made me wonder why they put them in the game at all. I am not penalizing them for the song choices specifically (All American Rejects, really?), but I am rather wondering why they included songs that are not inherently "Guitar" oriented. Those songs might be fine for Rock Band or World Tour, but the solo Guitar Hero games were about legends and masters of the instrument. So instead of getting more Steve Vai or Jimi Hendrix, you get Fall Out Boy and Jimmy Eat World.
On a personal note, I am really disappointed that they didn't include ANY metal. (The Darkness does not count, nor does Linkin Park.) You don't have to like the genre, but it is hard to deny that those were some of the most fun and challenging songs to play in the past games.