Low-res platfomer / stacker look mostly good to me. The only thing that doesn't is the green pixel in the low-res platformer at the front of the hat; I think that should stay in one place, or at least not be as bouncy.
High-res glider and miner are great now!
5th frame in the high-res digger animation doesn't fit well - try it in-game using the high-res experimental and you'll see what I mean. Basically, it looks like the lemming's left arm* (or right arm, in the left-facing animation) suddenly jumps to a different position for one frame. Also, the positioning in the PNG is slightly off, and the destruction particles should be RGB 255, 0, 255 (they'll then be recolored by NeoLemmix during gameplay to the appropriate color for the style). These things aside, looks good!
* from the lemming's point of view, not the player's
I've attached a version that fixes the positioning and the particle color, but it doesn't fix the 5th frame - that's something that you'll do a much better job of than I could.
We also need Xmas versions of both resolutions - and then I think that's the high-res / directional sprites finished (pending feedback during the RC phase, of course).