After 20 minutes I can say that Sonic Mania is fun, but I suck at it.
You know when something is fun but you keep losing so you kinda have less fun? That’s me.
I'll show you something
KMDP said a few months back.
I'll also refer you to The Geek Critique's excellent video on the subject:
The thing about Sonic that new players have to come to grips with is that he's "heavier" than characters like Mario and Megaman in a gameplay sense; it takes more time for him to accelerate and decelerate. His unassisted top speed is also much lower than his potential top speed. What the Mega Drive games and Mania have you do to reach higher speeds and to reach them quicker, is use the game's physics and level design to your advantage; and because Sonic is heavy, stopping (either on purpose or because of some obstacle) is more costly, so there's more emphasis on keeping things moving smoothly. Because Sonic has mechanics that allow him to exceed his unassisted top speed (holding down on the directional pad to roll) moving smoothly from obstacle to obstacle can increase your speed even further, rather than simply maintaining it.
Spin Dash for example isn't really a momentum-based move, but it's balanced against the rest of the mechanics. It requires the player to come to a stop (which, as I said above, is costly; the Spin Dash may not make up for the cost of stopping) and charge it up (which takes up some time), and its top speed is still less than the player can achieve through proper use of physics and maintaining momentum. It's a useful tool, but it doesn't dominate the gameplay.
The Drop Dash, which was introduced in Mania, according to The Taxman (Christian Whitehead) actually came about so that players can maintain their momentum and keep the flow going without having to constantly stop to charge up a traditional Spin Dash.
So my advice would be to actually keep replaying those first few stages to get accustomed to the games' physics and flow. Cram Green Hill Zone into your brain so much that traversing that terrain becomes second nature. Try out the other characters because Tails and Knuckles have a sort of flashy practicality that Sonic lacks, with abilities that let you 'break' the game in a sense to surpass several areas and access new ones. On the other hand, there are players that prefer Sonic not having any "crutch" abilities. The Insta Shield and the Drop Dash are small tweaks geared toward more experienced players that they may have a lot more fun with than Tails and Knuckles's abilities, while guys who like exploration and finding secrets will always be drawn more to Knuckles and Tails.
Mighty and Ray are odd ones; their abilities are slightly more obtuse and intermediate. You can't cheese the game as easily with them unless you really master their abilities.