You can compare with brick count/loading, bandwidth usage, fluidity of controls, graphics, stability and numerous other points of data. I'm not going to directly attack Roblox like some people do. Actually, that's a lie. Roblox users and defenders are like creationists. No matter how outdated their beliefs are, they cling to them in a desperate hope that they're right and that one day there will be a definitive fact that proves the other side (evolutionists and/or Blockland users) wrong.
I don't see the comparison. Nothing built with OGRE and cobbled out of Internet Explorer's framework is ever going to be as good software-wise as a game built from even the aging TGE-A. This is coming from somebody who has had experience developing for both web and TGE/T3D.