Since the source is up, I've been playing around with a bit ahead of the official demo. I intend to do more tomorrow, but I couldn't help doing a little tonight. Time to nitpick!
Performance / Controls
1. Camera rotation seems to be tied to the framerate in some way? When the framerate is extremely high (over 1000 FPS), mouse rotation becomes extremely low sensitivity, where large mouse moves barely cause a rotation, but when I cap the framerate to 120 using the nvidia control panel, the sensitivity feels much more normal. Doesn't seem intended.
2. The game hitches for about an eighth of a second every 2-3 seconds, but inconsistently. I thought maybe it was doing it when it reads and prints the FPS reading to the console, but it doesn't always line up with that. If the camera is moving or rotating during the moment a hitch happens, it 'keeps its momentum' during that moment, causing the camera to suddenly jump. The effect is greatly exaggerated (multiplied?) at high FPSes, causing such hitches and jumps to be extremely noticeable. Hitches can be observed just by waiting on the level selection screen or level preview too, but seem to be much more infrequent compared to active gameplay.
3. Although the game physics are capped at 30 FPS, the rendering isn't, so currently the game maxes out the CPU core or GPU (whichever ends up being the bottleneck on the given system). This is fine currently, particularly since the FPS is useful for assessing performance at this stage, but consider adding an actual Frame cap or Vsync in future for people who don't want the game using unnecessary resources.
Blockers / Turners
4. In L3D, assigning a blocker or turner would cause that lemming to become a blocker/turner at the edge of that block no matter what. Currently in Loap, if you assign the skill in the last quarter or so of the block, they'll keep walking into the next grid square before becoming a blocker/turner. Visually, it looks like you moved the turners away from the block edge, so I suspect this is actually an intended change, but I wanted to make sure? If this change is kept, it might be worth considering if any puzzles are impacted by this (e.g. assigning blocker/turners directly out of a fall from a ledge / builder bridge for instance).
5. Following on from #4, if you assign a Turner to a lemming that is about to fall off a ledge, the lemming will not become a turner (either on the ledge, or after they land) but the Turner skill will still be consumed. This is probably true for Blockers too, but I didn't confirm for sure.
6. Related to #5, if a lemming is between two blockers on the same square (e.g. by assigning a blocker either side of the starting hatch), then Loap lets you attempt to assign the trapped lemming as a blocker and consumes the skill, but they'll never actually become one.
7. In L3D, if two lemmings were bunched up, assigning one of them as a turner while they were in the first half of a grid square (in the direction of travel) would cause the turner to turn the other lemming. This trick is used in LP3D Wafer Walkway, for instance. Currently in Loap this doesn't work - the trailing lemming always ignores the turner and goes through, even if you assign the turner as early as possible, as described in #4.
8. In L3D, two turners on the same grid square pointing the same direction could be used to simulate a blocker, and two pointing into each other would catch and compress the crowd. Neither trick currently works on Loap. Lemmings will turn at the first turner they encounter, and ignore all subsequent turners on the same block, walking through. Turners inside of splitter blocks or immediately adjacent to deflector blocks are ignored in the same way.
9. In L3D I don't think you could 'overlap' a blocker and turner by assigning both to the same edge. Currently you can in Loap, as seen in Attachment 1. I might be misremembering, though.