firstly when Luke is initially attacked by the Wampa whilst on his taun-taun, and we briefly see it's face as it lunges into camera, something about the way the shot is framed ruins it's whole sense of scale and it ends up looking like a muppet sized hand-puppet and just appears badly inserted into the scene, not to mention it looks nothing like the special edition Wampa footage from the cave (which I don't mind the new footage). I don't know how talented anyone is with creature animation, but even if the original shot could be reframed to make him appear much larger and ominous and perhaps give his face and eyes a bit of articulation to make him look less puppet like.
secondly there's a brief shot during the Hoth Battle, I believe it's when Wedge (?) is flying around an AT-AT's legs with his tow-rope, there's one quick shot where the screen is framed by an AT-AT's Legs and a snowspeeder makes a pass across the screen behind the legs of the Walker and apart from a few wispy clouds it looks like they left the Bluescreen in the background and didn't matte in the proper sky background (ie. the sky is a very bright (bluescreen) blue) again it's a very brief split second shot that probably a little colour/saturation tweaking would fix and make it match the colour of the sky in the rest of the scene.