I can unclip my right foot no problems, but my left is sometimes "sticky." the motion just seems very unnatural.
One of the things I've done over the years is when I get new SPD cleats is to take a Dremel tool and deburr all the edges of cleats. If you take a look at your cleats you will notice really bad machine/stamp markings and nasty edges from the manufacturing process so if you deburr and smooth these out along with the pedals you will be amazed at how buttery smooth clipping in and out gets.
Also check to make sure the spring tension in the pedals are equal from right to left.