Play the Genesis/Megadrive games again, if you like platformers then you'll probably love them (though you can skip Sonic 1 as that's somewhat finding it's footing).
The appeal of the classic games lie in both the music and visuals as well as the gameplay. A lot of people seem to forget that you don't have or should be running the whole time, indeed the nuance of the games in comparison to Mario are that they don't have a run button, at least in the sense that you can instantly switch between high and low gear. Sonic is about gaining momentum, speed can be a thrill but can also be a hinderance if you're careless.
Really it's a series that rewards multiple playthroughs, as one practices and improves you'll find it becomes immensely rewarding.
As for the current games, well, that's a different kettle of fish.