Nice to see this game get brought up here.
I have a LOT of things to say about it, a lot of mixed feelings, a lot of things to like, a lot of things to not like (in fact, I'm planning to make a video essay about it like the J2ME games now that it's available on the Microsoft Store... for some reason). I won't wear you all out with every thought I have, but I'm happy to share some of what keeps me playing (and my biggest specific gripes), as someone who's been playing it on-and-off for a couple years by now.
I don't mind the Energy system too much; it is an artificial limit to playtime, sure, but I like how it incentivizes solving levels
efficiently even without fixed skill counts. It opens up more options for solving a given level, allowing the player to reason out which one(s) will minimize energy use or minimize the risk of lemming death.
Also, the game introduces new skills (yes really!) the more you play. Sadly only 2 out of 5 of them are available without having to pay, but they are mostly interesting and have different energy costs to consider. The most surprising thing about them to me is that NONE of them originate from L1 or are boring variations of L1 skills! We have tile-based equivalents of L2 skills in a modern Lemmings game!
The "Challenge" levels introduced each season are a fun way to break up a monotonous world; the goal is not to solve them efficiently but simply to get all your Lemmings out alive, as using skills does not cost you energy in these levels. Sometimes you do get a pathetically easy one, but most of the time you have to really think through your route and/or be very careful when navigating. You only get a limited number of attempts at playing these levels--not in the sense that there is an absolute maximum number of chances throughout a season, just that chances are hard to come by--so the pressure is on.
Even more fun than the Challenge levels though are the Mayhem levels, which are previous seasons' Challenge levels with different additional rules. Some rules are annoying (random portals, gross) but among these are a simple time limit and a STRICT energy cap (independent of your main-game energy) which feels VERY classic and I quite like it. The energy capped levels are some of the most fun times I have playing this game.
All ads are indeed optional now, which is super nice. Most of the prompts you see between are only asking you to watch an ad for extra Energy or Lemmings, which I'm fine with. Admittedly, I'm not above watching an extra ad here and there to extend my playtime or to get through an annoying world faster, especially considering most (but not all!) levels are procedurally generated...
Speaking of which, here's my biggest problem with the game as it is. It's not THAT most levels are procedurally generated that's the problem; it's a necessity to make a game structured in this way work. What bothers me is how the few hand-crafted levels are distributed across the game. Almost always, you KNOW when you get one, as they tend to have unique terrain layouts and are sometimes even genuinely really clever puzzles. These really serve to break up the monotony of some of the worlds; it's always a pleasant surprise to see one. The problem is that when you start the game, you barely get any of them for a long time. And I mean a LONG time.
The first 4 worlds of the game each have a fair amount of hand-crafted levels. They're pretty unremarkable, but they're designed to ease the player in, because that's just good game design. After that, there are a few tutorial levels to show off a couple new mechanics and a couple "hand-crafted" levels that only exist because the procedurally generated levels they replaced were accidentally impossible to complete; they're procedurally generated levels with, like, one or two troublesome blocks removed. Aside from those unremarkable exceptions, the player goes through. NINETY. FOUR. WORLDS. Before seeing a SINGLE hand-crafted level. That is several months of your life assuming you're playing pretty frequently. That is a LOT of time for people to decide that the game is boring and never touch it again. I've managed to make it out of that drought, and from what I've heard the newest worlds they've added have TONS of well-made handcrafted levels. That's good that they're focusing more on those now, but it will take me LITERAL YEARS to get there. For most people, that time investment just isn't worth it.
Regardless, I do have fun with the game and think there's a lot to like about it. It's definitely flawed in a lot of ways, but it's not soulless.