For Sonic Frontiers....I'm definitely waiting for some reviews, to see if they screw it up first. When you manage to botch a port of Colors, you don't get the benefit of the doubt. (I know that was technically handled by a different studio, but it still doesn't look good.)
Sega's actually overdue for a good Sonic game. They usually have one per decade or so. And Mania wasn't technically the main team. The last good one was probably Generations back in 2011. And they've taken their time on this one. So...fingers crossed!
Mind you, Sonic Origins is also coming out the same time as Frontiers (flashbacks to Mania and Forces), and despite the backlash to the DLC/preorder plan, I actually expect Origins to be pretty great, once it releases (and the physical version comes out). So...hopefully Frontiers won't compare horribly to the 2D game.