Yes, the game I swear I've seen many say ended up looking better that that CGI-rendered trailer.

Yeah I've seen a lot of folks claim this too which is insane. I think the final game's more stylised look with heavy post-processing kinda skews people's perceptions and smooths over the downgrades to characters, animation, smoke, modelling, etc.

You may be right. I haven't compared the trailer and the game properly, but they look very comparable to me. I took another look at a comparison video, and while some aspects look worse, some look better. Perhaps with a more in-depth look, one could reach your conclusion.

The CG trailer was rendered offline with unlimited render time per frame so it's not really a fair comparison, but stuff like the number of polygons poured into the characters, the billowing smoke and flames, etc are just way beyond what a PS3 could realistically do in a working game. 

The final game LOOKS more eye-catching in some ways not cos its more advanced, but because it leans into cool-looking tricks like colour grading, depth of field, bloom, etc.

Both screens look grey and blah to me.

Another one that really stands out to me is Mario 3D World, which looked incredibly safe, basic, even generic in its reveal trailer at E3 2013, which barely showed any of its variety or creativity. Later trailers and the final game were much better than that underwhelming reveal.