Just got Transformers Devastation and it's my first character action game and I'm loving it. So now I'm thinking about picking this up at some point down the line. Would this be a good next step into the genre, or would something like DmC special edition be better? Also is this game good outside of the sheer mechanics? I value stuff like pacing, encounter design, boss fights, level design, atmosphere and art direction, etc pretty highly.
Honestly, I think that either Bayonetta or DMC3 would be the next best step for you.
DMC4, while a true gem, is rough around the edges when looking at it from a level design and pacing perspective. There's excessive backtracking and ill conceived puzzles. The bosses are great, but you have to fight them multiple times. Visually, artistically, and mechanically, it's top notch, but it does have its share of problems. I don't want to shy you away from getting DMC4SE eventually, because I think it belongs in everyone's library, but at the same time I'm not sure if it should be your next game.
DMC3 is a complete package to me. It's paced well, has a compelling storyline, interesting characters, and withstands the test of time gameplay-wise. Some people prefer DMC3's gameplay to DMC4's, as they are very different when it comes to weight, inertia, and cancel windows. You can either get the HD collection, or you can get the PC version. Be forewarned that the PC version is a pretty poor port and a resource hog, but you can get it running perfectly with a little work and patching. People here can help you.
Since you've been playing Transformers, Bayonetta should feel more familiar to you as a Platinum game. Control-wise, I understand that they're similar, though Transformers is simplified.