Watch 2001 in 1080p with Dolby TrueHD and tell me it's not a vast improvement. If you do, you're either lying, partially sighted, or just plain stupid.
Last week I watched 2001 and it looked so pretty it almost made me weep.
My first blu-ray purchase. It's like seeing the movie for the first time. Since getting a blu-ray I'm much more interested in old movies and TV shows like trek than I am in any new stuff.
Like you say, it depends on the movie. So far, the clearest most amazing movies I've seen in HD on blu-ray are 2001, Patton, and Casablanca (abso-freaking-lutely stunning). Robert Wise's "The Sand Pebbles" looks pretty sweet, too.Older movies aren't going to have that certain "pop" that you'd get with Transformers, Pirates of the Caribbean or whatever, but some studios really don't put a whole lot of effort into cleaning up older titles (Universal threw a lot of crap onto HD-DVD like Mobsters, while Field of Dreams was bad on HD-DVD and they made no effort to fix it for Blu-ray), and when they try to, the digital noise reduction actually makes it worse. For an "older" title, Blade Runner would be my example of doing it as best as possible).
What's really amazing about the added detail is how much of a sense of depth it adds to the picture. It makes watching older movies a whole new experience. Standard definition looks flat by comparison.