Never really grew up with Sonic, played Sonic 1-3 and others years later on the PS2 collection and generally enjoyed them, although I had my problems with them. Freedom Planet is basically my Sonic, so to say, as I feel more connected to FP than Sonic, despite only having 1 (now 2) games. That's how solid Freedom Planet is.
The game obviously takes inspiration from Sonic, Gunstar Heroes, and some other games. Played Gunstar a bit later after FP, loved that too.
Hands down, one of the best things FP does over Sonic (and just in general compared to a lot of 2D platformers) is that enemies have to actively attack you in order for you to receive damage. Instead of 80% of enemy attacks just being contact damage, and when there is contact damage in FP, there's a good reason for it, like the enemy is spiked, or it's on fire, etc. Also, in FP, you have a life bar, and can take a fair amount of hits, and get health pickups, which is great, because getting one shot in a Sonic game just cause you don't have any rings gets old real fast.
The combat's pretty decent (a bit better in the sequel), the music is memorable, the bosses are neato, and the stages are rad. The stages can stretch on for a bit too long at times, someone dubbed it as "Freedom Planet Syndrome" where a level in a platformer stretches on for waaaaaaay too long, which I don't really have a problem with usually, unless it's stupid long. Klonoa 2 did this over a decade earlier, where some levels are like half an hour long, while most levels are like 8-15 min long. I'm sure there's a bunch of other platformers that do something similar.
The protagonists are very charming and memorable too, and have fitting voices to go with their personalities. There are 3 different playable protagonists, each with their own playstyle, mostly sharing the same levels, but have some levels unique to each of them.
Here's to an eventual release of FP2 on GoG as well, as I'm allergic to Steam, but bought it on there anyway.