Overall, I'd recommend anyone who hasn't played Sonic Colors to get Ultimate, since it is basically Colors but with more content. The finale of Colors is memorable and exciting, and even though the wisps go on to be unwelcome additions to Sonic games games after Colors, they were and still are a fun part of Sonic Colors. Having said all those negatives, there are positives. Not to mention, for a 3d Sonic title game, over half the gameplay time it actually 2d. Only people who really want to acquire all achievements would see any worth in playing through those levels again. Unfortunately, only the first level of every act is really any good, and the rest were very apparently made to extend the gameplay length of the game artificially. That would be great, if most of the levels were fun to play through. But this is Colors Ultimate, and it does have more content than the original game with unlockable cosmetic option to encourage replaying through levels. There's a feeling of cheapness about Colors from its writing, cutscene animation, to the amount of content it originally had. In retrospect, there are a lot of flaws about the game that are very hard to overlook, things like the incredibly short campaign that takes maybe a few hours at best to complete. In fact, it was viewed as a refreshing change of pace to the games that came before.
There's a bit of a perception that Sonic Colors saved the Sonic franchise when it came all the way back in 2010. There's a bit of a perception that Sonic Colors Sonic Colors was never really that great, but Ultimate is both a downgrade and an upgrade. Sonic Colors was never really that great, but Ultimate is both a downgrade and an upgrade.