Just finished my review copy of the Wii U version.
My full review is forthcoming, but I honestly really enjoyed myself and had a lot of fun through most of the game. It's a mostly great game dragged down by some major inconsistencies and unfortunate low points that dilute the experience -- mainly the Wisps/Color Powers (which are so obviously tacked on and should never have been in the game at all), incredibly weak boss fights (including the final boss), and almost all of Frozen Factory.
But when those elements aren't dragging down the experience, the core gameplay is really solid. The Galaxy inspiration is very obvious, but it's much more than just "Super Sonic Galaxy" - it makes its own mark.
The game is an audiovisual marvel, too. Besides The Wind Waker HD, I'd say Lost World easily qualifies as the most beautiful game on the Wii U and definitely one of the best-looking, most vibrant games I've played this year. And while Sonic games almost always have some of the best music around, that doesn't take away from the fact that the soundtrack is just stellar. There are so many excellent songs it's hard to pick a favorite, but if pressed I'd say the Tropical Cost 3/Lava Mountain 2 (rail levels) theme takes the cake.
The writing, voice acting, and story are also high points and stand out in a good way. The dialog is especially sharp and the story gets surprisingly dark (for Sonic) at times -- it never feels too juvenile and there's just enough weight to the proceedings that you keep wanting to find out what happens next.
Also, the game's challenge has been far overstated in the "professional" reviews. It's really not that hard a game, but it does demand that you learn its mechanics. You can't bullshit your way through, but it's not unfairly difficult either. Personally I found Colors quite a bit more difficult than this (in a bad way).
That said, the game could really do with some tutorials. Even having finished the game, I have no idea quite how horizontal wall running works and I haven't even begun to figure out how to get the Red Star Rings that require that skill.
Still, overall I'm quite happy with the game. It's certainly not perfect, but it's a worthy Sonic game that upholds his return to glory following Unleashed, Colors, and Generations.