I've said it since Wind Waker: consistent art direction trumps HD any day of the week. My absolute favorite game in terms of art direction is the Patapon series. Iconic, colorful, consistent, animates beautifully. For a more complex thing, I'll take Rayman Origins. Absolutely stunning game that benefits from HD because it USES the technology to its benefit. It's not required (the game looks perfectly amazing at 720p) and still looks mind-blowing. I've seen Skyrim played in HD and at 720p and it doesn't look all that different to me.
Now, take some of this generation's Nintendo games (like Other M, Metroid Prime Trilogy, Mario Galaxy games, and Skyward Sword) and pump them onto their native HD resolution, and I think they'd all look absolutely incredible.