I'll also vouch for Okami. It's one of my favourite games, it's freakin' amazing, one of the best games I've played. The story is engaging and manages to be cute and bleak at the same time, and it just looks great. Games will push a higher poly count than Okami, but Okami will always look good because it's so unique.
It's a huuuuuuuuge game, it takes about 35 hours to beat it your first time around, and the whole time it manages to be engaging. I never got bored with it during the entirety of the quest. If you like adventure games, you'll be all over it.