There are a whole lot of styles that I'd like to be gone - plus over 33,000 files along with them. I'd like to have only L1, L2, L3, and SMS Sega styles only. What happens when I delete the others? Well, I get an error message and cannot play the levels.

Make sure you're not deleting the "default", "xmas" or "special" styles. In particular, NeoLemmix will not take kindly to the absence of "default" (the other two won't cause problems until you try to play a level that actually uses them), as it contains several objects shared between multiple styles (eg. the common hatch and water shared by Dirt and Pillar; the generic recolorable one-way-arrows) and the placeholder pieces used as fallbacks in preview images if pieces are missing, not to mention the actual lemming sprites. Xmas contains the lemming sprites and objects from the Xmas/Holiday Lemmings games (the terrain pieces are mostly identical to ohno_snow, and the few that aren't have been merged into ohno_snow in NL), while Special is for the special graphics levels (like A Beast Of A Level).

(It is technically possible to create a level that doesn't need the default style, but it's easier to just assume that every level requires it.)

At any rate, if you're distributing your content you only need to distribute the levels, music, and any custom styles you make for it (if you don't get these added to the Style Manager / all styles ZIP). People looking to play your packs should already have (or easily be able to obtain) everything else. You certianly don't need to include every style that exists.

I will also note that if we're still on 12.12 when this feature is ready, I'm quite happy to release it as a minor update if it merges (or cherry picks) fairly cleanly. If not it will need to wait for 12.13.

Really? What was the system?

Based on a skim of the code in an old commit that still had it (77ae002 is the one that removed it), you'd begin the level with 50,000 points, and your score would decrease based on certain things happening (but could never drop lower than 100 no matter what). Where one of the penalties implies another (eg. "level failed" also implies "didn't save 100%"), the lesser penalty still gets applied as well.
Level outcome
- Failure to meet the save requirement: -10000
- Failure to save every lemming (including Cloners): -1500, and a futher -100 per lemming not saved

Time penalties
- Prior to the first lemming being saved: -2 per frame
- On or after the frame where the first lemming gets counted as saved: -1 per frame

Skill usage - Each time a skill is used, the corresponding deduction is made.
- Walker: -10
- Climber: -25
- Swimmer: -35
- Floater: -20
- Glider: -55
- Mechanic: -40 (now known as "Disarmer")
- Bomber: -20 (plus the penalty for losing the lemming)
- Stoner: -15 (plus the penalty for losing the lemming)
- Blocker: -25
- Platformer: -90
- Builder: -120
- Stacker: -45
- Basher: -50
- Miner: -50
- Digger: -50
- Cloner: -200
- (The Fencer, let alone the Shimmier, Jumper, Slider and Laserer, didn't exist yet at the time scoring was removed)

Other
- Triggering a trap: -150 each time
- Increasing the release rate: -100 the first time, no penalty after that
- Decreasing the release rate: -200 the first time, no penalty after that


The score was displayed on the postview screen, and high scores were saved. No one ever really paid much attention to it, so it got culled (technically as part of the major cull / tidyup between 1.43 and 1.47, although it got merged into stable versions a tad earlier, with the score first removed in 1.43-C).

Even more important than what WillLem mentioned as focuses, is looking for any bugs. In particular - does it pause when it shouldn't, or does it ever not pause when it should, does it interact properly with skips past the frame on which the last lemming is removed (in both directions), etc.

Neutrals should not be treated the same way as zombies. Although no skills can be assigned to them, they could still be saved if they have a path to the exit, or possibly via RR manipulation or nuking.

My reasoning on the option to disable it even when the save requirement is met is that it gives the same convenience to people who may be aiming for talismans or max-saved solutions etc.

I wonder if the option to not auto-exit even when the save requirement is met, should be added?

In no way is accepting it conditional on any particular behavior here; I just thought it's worth raising.

If code for this is developed and tested by the community, I'm happy to merge it in. If there is significant divided opinion about whether this change is desirable, I will only merge it if it's implemented as an option rather than the sole behavior (being enabled by default is acceptable).

If I can achieve windowed fullscreen in general, I don't see why it wouldn't be possible to support both. The bigger question is whether I can fix the load replay issue in true fullscreen.