Kingdom Valley Act 1 is my new favorite Sonic level.

[EmeraldFoxDeity]

Just what the title says. I'm baffled myself really. It just felt so thrilling to me. Mind you I haven't played the HD Unleashed so one of their day stages could be better and I've yet to experience peak. But for me at least, right now this is currently it. Granted I did get just as far as this level so far so a later level my surprise me. But for the moment at least this is incredible. Did not expect anything originating from Sonic 06 to be this good. Especially with Sonic's Crisis City being just kind of eh. Especially his Act 1. Kingdom Valley Act 2 isn't bad either, but it's a 2.5D stage so, ya know.

[$OULJA $TRIFE]

Its definitely the best 3D boost stage, only things that come close are Seaside hill (modern) Rooftop run (both versions unleashed and generations) and maybe Jungle joyride

Kingdom valley is by far the most polished stage 3D sonic has ever done

[GrimAtrament]

best boost level certainly. kingdom valley is very good,
if we're talking strictly sonic 3d levels
SA2 final rush/crazy gadget/metal harbor SA1 speed highway, red mountain, final egg, twinkle park, lost world( the level not to be confused with the game lost world.)
is still higher.

[cm pls]

its okkk

[Mez Koo]

If you have the original sonic generations on PC you can install the unleashed project to play the unleashed boost stages in Generations. They're really good and worth figuring out how to install.

[Axelhander]

It's my favorite as well, and I wish Act 2 was more of that instead of the forced 2D thing.