Yeah, there are others but I can't be bothered to remember them. I don't know what everyone likes about Sonic Robo Blast 2. I just don't think it's a great game. The movement doesn't work for a Sonic-style game, levels are giant and empty, it's just all-around weird.
Honestly, I've always thought the game was ok, but not spectacular. Honestly, the entire draw is the modding potential. It's really that kind of game that gets me playing it for a little bit, and then getting bored and getting back to procrastinaing my projects.
It uses the Doom Legacy engine, which is how it can have "3D" floors (not normally available in Doom, but then a port of the source code called DosDoom, which later became the awesome EDGE*, developed them. Legacy then got them later on). I discovered this years ago too, but through the Doom community not the Sonic or Klik communities. Oddly in the Doom community another sonic conversion where sonic uses guns (ie, it's a lot more like Doom, and first-person) is far more famous. Probably because it uses the Zdoom port, which has become the de-facto 'standard doom engine' somehow.
*-EDGE was once supposed to become an engine in it's own right for making your own Doom-like games in (in other words a 2.5d version of FPS creator but far more flexible). In fact it's probably possible now with some workarounds - i wonder if an EDGE game would go down well on TDC? .