I would say the addition of pink slimes and all the slime variants are surprising. I have not seen what all of them do but the addition of the pink slimes makes my head spin. They throw out almost everything we know from the original game. Already I'm seeing a strategy here: Going right to pin down the first set of slimes, then going left to pin down the other set later when resources have been accumulated.
The only overarching issue is the lack of hanging bridges to connect to the left side slimes. Rather than having to go through the tedious process of building hab walls to make a bridge that hopefully doesn't get broken all thanks to the overhang leaving a gap near the entrance for balancing purposes.
Again, however, we just have been introduced to Area 2 which I have not really gotten into yet. So I'm going to make a fresh save to redevelop a strategy for this that works. Either that or just try to continue my current save.
As for difficulties here's how I've thought of it: the current difficulty can be seen as the veteran/ hard difficulty as it should be challenging but also fun for players who have feel underwhelmed by hard in the original. As much of a masochist as I am I can tell that this game needs some difficulty adjustments that will come at some point. The addition of the flying slimes can feel kind of overwhelming to new players. Even as a returning player I already see that these pink slimes are going to be the bane of my existence; Somehow, these things make white slimes look passive. I mean that with what few instances of pink slimes I have encountered. These things already require you to have more lasers than you can produce consistently by the time they appear. I was on mark two lasers when I was first attacked by these things.
White slimes makes more sense for the first layer as it is highly unlikely you'll be directly going towards the slime spawners. It's usually better to actively ignore the slime spawners and save it for end game, or in this case prior to area 2.
Pink slimes fit perfectly into the vertical nature of area 2. Rather than having several slimes at once bombard you, these droppers would require more precise methods. It would make more sense to have these as sentries with a unique spawner to give the slimes more pushback to force you to check on the spawners rather than just putting up an energy barrier, a laser and calling it a day.
I'll give more feedback when I have more time to play with a clear head. It's like 12 am for me.