I have an m-audio Keystation Pro 88. It is all I can afford at the moment, so I'm stuck with it, but I am curious about how a better keyboard would respond.
I played a baby-grand steinway growing up, and I remember how it used to play.
On my m-audio keyboard, I have two problems that bug me the most:
1) playing really quietly still allows the piano to play a note - on a real piano, you have to press with a certain velocity, or nothing will play at all. This doesn't bug me nearly as much as the following one, though:
2) On the m-audio, if I play moderately loudly, the keyboard sends a 127 (max) velocity to my computer. If I play very loudly, it has no higher place to go, so it still sends a 127. The keyboard itself has velocity curves that i've tried adjusting. This doesn't fix the problem. This seems to be a physical limitation of the keyboard itself. It can't physically tell the difference between moderately loud and very loud playing. Would a more expensive keyboard fix this problem? There is something very satisfying about being able to bang really hard on the keyboard and have it produce a very loud sound.
I tried one of those out once. For a piano feel it pretty much sucks.
I'm looking at getting a Yamaha P85 for a short term portable solution as my studio will be at the top of some steep stairs. Later I'll probably move up to a graded action unit to replace my Yamaha digital grand.