Hell, I'm the only one attempting a mod of this scale at ALL =P The only "other" SASRB2 is the one on SRB2 Add-On (also by me), which is just a basic header hack.
This (more or less named "SASRB2 v1.1", to corrispond to the fact it's a new version, plus it uses lots of SRB2 FD1.1 features) does much more -- it changes a lot of the maps, retextures almost the entire game, adds new music, changes how the enemies act, and provides a whole new storyline.
It'll be about five or six maps long (two of those I'll have to create by myself) and feature one brand new boss (Chaingun Eggman), plus tweaks to the Egg Slimer. And, of course, there will be a Super Sonic sequence if you grab all the Chaos Emeralds. I'm even pondering remapping the special stages.
There will also be an Adventure Field (which I've just started work on) for those of you who want to wander around aimlessly.
If you want some screenshots...
So far, the GFZ stages are the most edited of the bunch; GFZ1 has been extended in length, for instance, and GFZ2 is engineered to play completely backwards to what it plays like in the regular SRB2. Almost every GFZ texture has been replaced.
The Eggman boss has been reworked as well. No longer can he be beaten in 20 seconds; once he sees you he will open fire with his chaingun -- beat feet or become swiss cheese! When you see an opening, smack him one!
At first it appears not much has changed in Techno Hill Zone, and truthfully, not a lot really has. Act 2 has recived a completely brand new set of textures, though!
Castle Eggman was not pictured because I don't think I'll use that in SASRB2, and the Egg Slimer boss was not pictured because I didn't change anything but the textures. The Adventure field also was not pictured because I only started work on it like.. yesterday.
