I think it would be nice to have like an overworld shot in the background instead of Jade Gully. Just my opinion. As for the rest, it would probably look better once rendered in 3D by Andrew. The concept isn't bad, I'd just need to see it in full implementation to be convinced.
As far as the sketches go, they seem too Generations to me. Sonic jumping out of the ring and manually navigating around instead of a traditional menu just doesn't seem 90s to me.
My personal idea is this:
*Open with a casual, non-flashy disclaimer talking about SEGA/Sonic Team's property blah blah blah and SEGA Technical Institute blah blah and maybe a special thanks to Chris Senn for all of his contributions.
*Instead of SEGA popping up in the old fashion, put "AXSX" there instead and maybe have a similar synthesized voice say "AX-SIX". This is because, despite the game orignally being STI's, it was made pretty much from the ground up by the AXSX team with input from Senn and various sources. SEGA/STI had their screen before this, so why not.
*Next have some 90s intro, with Sonic jumping into a ring from a black screen, then the background flashing to something nice like a much higher resolution of the Jade Gully background (the mountains, not the actual level) or a world map. The title "Sonic X-Treme" comes in with some semi-fancy transition.
------This is where I kind of wanted to make a change to the whole thing. Instead of it being "Sonic X-Treme AXSX" or "Project AXSX", just have it say "Sonic X-Treme". The way I came up with this is giving the AXSX line its own screen, showing that it was the AXSX team who put in all the effort to let this game see the light of day. Despite it being AXSX it should, first and foremost, be recognized that the game is "Sonic X-Treme". Changing the title gives the impression that it's meant to be a spinoff or something that plays off the original game instead of simply being a faithful replication of it. Same game, same name.
*Starting from the title screen fades to black and opens with a generic, yet stylized menu.
+(From Load Game)
---Fisheye Distortion (slider, or just multiple options)
---Sound (volume for sound effects, music, etc)
---Rendering Distance (slider or multiple options. Sonic R for PC is a good example)
---Sound Test (self explanatory, but maybe having to unlock each stage/boss theme by playing)
---Cut Scenes (assuming they're used)
---Credits (Just plays the credits over a black screen)