I don't Steam but Sonic Mania is definitely worth getting if you're a fan of the classic Sonic games. Absolutely love it. It has one of the best soundtracks in the series history, it has the best collection of bosses in any platformer I've played (albeit, they're not very difficult but the unique and varied styles of all the bosses made them a joy to fight for me), and the level design is the classic Sonic formula perfected. Most importantly, the variety in level design is brilliant, pretty much every Act has some new kind of different platforming gimmick, allowing the game to flow cohesively through gameplay but still give each Act their own definitive identity. Chemical Plant Zone Act 2 is my favorite level in 2D/Classic Sonic. I also think Sonic Mania is the perfect example of how nostalgia should be used in video games.
Also, Sonic Mania Plus is coming out next month, and that's going to be five dollar DLC iirc for anyone who has Sonic Mania so I think getting it now is the perfect time.