Well, all of SMG easily for me, but I also have to say Sonic Unleashed's Apotos.
I'm not gonna lie, I've always been a huge fan of the Greek Isles. I have had Greek Isle calendars gracing my room for years now. I honestly don't know why I like them so much either, but that is besides the point. When all that Unleashed stuff got leaked in mar/apr of 08, I was like WHOAH when I saw ApotosI mean I was like "Sonic is in MYKONOS, FUCK YEAH!" and all that jazz. When the game actually came out, I actually took a good 12 minutes to
walk Act 2, the first real level, before actually playing it for reals. Petros the pelican was there, the sea was there, it was Mykono alright! Lighting looks so pretty too, I mean I just love the artstyle they chose for the game period, it is just such a pretty game! Anyways, when I played the level for reals, it felt like Green-Hill for the first time ever. Apotos was the new Green Hill to me, it just clicked. It was Pure Sonic, then at the same time it was totally Greek, and I was loving every moment of it.
Another pick for me would have to be something that needs no pictures, and that is the Courtroom in the Ace Attorney games. Sometimes when you get really into it, that simple sprite BG can be the most immersive world seen... Truly awesome when it happens, I know it happened during my play-through of AA3!
Lastly, I would have to say both NiGHTS games and Flower as a whole.