From an aesthetic perspective, I find par 4s that manage to be really difficult despite having no bunkers very appealing. The greens are frequently diabolical, and the approach shots demand great accuracy. Every time I play a hole that fits these criteria, I start wishing there were more of them. But then it occurs to me that a large part of the appeal of these holes -- at least for me -- is that they're rare and have to be selected carefully and designed/built with a lot of precision.
From TV, my favorite example is #14 at Augusta, which always seems to play harder than the more visually intimidating holes on the back nine.
What are some other great examples of this design strategy?