Overall, Sonic Mania Plus is a great game.  While the Plus part really only gives you two new characters and a harder version of the game, current Sonic Mania owners will only have to pay five dollars for the DLC which isn't too bad.  Even 30 dollars for those wanting a physical version is still worth it for the main game alone if you don't already have it.  Either way, fans of Sonic who haven't played this yet should definitely pick it up at some point.