Since I played the first playtest, I'll try to list the improvements I experienced with this second playtest.
First, the overall balance of the game is much better than the second. With more towers to try out, there was definitely more choices and experimentation we can play around with the tower combos and placement. However, I did feel like some description for each tower would be nice since some of the time was figuring out the range and what the tower actually did rather than finding the synergies and their effectiveness against certain enemies.
The level design and flow was easier to grasp initially so good work. However, the collection of the stardust is still a bit of a chore, even with the added tower to aid with this. Like some others said, it is still mundane enough to affect how we played the level, like putting towers closer to the chest to speed up the collection process. This might affect how well the towers were able to clear the waves if there were no clear winding paths or choke points.
The level layout was a nice touch. The different groups of levels were nice, especially the 0 levels that showed the player the basics of the game, like feeding the blackhole stardust to complete the level. The improved UI also helped, and the extra shake when the enemies moved past your towers and drained the health was a nice feature (not sure if was present before because of the busted Saturn tower in the first playtest).
The level art itself was interesting to see, especially the different enemies that appeared in the different terrains (like the snowy field). Even though the level structure is pretty similar and there doesn't seem to be interactable or added effects, the different field map provide a change of scenery to an otherwise similar experience across different levels. It would be cool if there were terrain effects that changed how the towers are able to deal to the enemies (like a certain elemental affinity is boosted while another is resisted, like boosted fire attacks and weakened water attacks in a fire terrain). I haven't played much with the elemental attacks but it would be nice if we got a list of enemies that may appear in a given level, giving us a better way to prepare instead of purely experimenting with the different towers available.
Finally, thanks for putting the frame rate cap. I could play the game without worrying about toasting my machine.