Knoebel's is one of the best classic parks around.
Phoenix is a great coaster, especially at night - offers some nice airtime and its not rough.
Twister is good, I've never gotten a top notch ride on it, others have raved about great rides so your experience may vary.
Food is awesome at Knoebel's - Pirogi's, Caesari's Pizza, White Birch Beer - its all good. And its cheap. Try everything, don't think you'd regret it.
Knoebel's ride operations are fast, lightning fast - Phoenix and Twister have the fastest loading times I've ever seen on a coaster, people get out and the new people board, get restrained and checked in a matter of seconds.
I'd recommend staying as late as possible for better Phoenix rides, to get the coaster option wristband if its available and to eat and have fun - not too many of these type of parks around and Knoebel's is one of the best.