Among 2D platformers in general, I think the medal for best movement feel goes to the Fancy Pants Adventure series. (You can still play it online on sites that have Flash replacements, start with the 4th game because it has everything.) But that's a deliberately easy game, you just run through the levels and have fun.
Among difficult precision platformers, I'd say the N/N+/N++ series has the best movement. (The first game is also still playable online.) Be careful, this one is like a drug, it has a huge number of levels and it's really hard to stop playing.