I've been promising an effort post about Arknights. Here goes!
Arknights is gachapon + tower defense. Your pull-able game pieces are characters, called Operators, whom you deploy to a coordinate grid to defend your base against waves of enemies. Each has a role, like Sniper or Medic, that describes their main use case, and they vary across several stats and have unique skills to activate. I don't want to say it's inherently more complex than a more typical JRPG gacha--high-level play in those can get quite cerebral--but at least the possibility space in early- to mid-game is more varied. What Operators do I bring for this mission? Where do I put them? When, in what order? Which direction do I aim them? Subtle differences in decision-making can make or break a level.
Star ratings: 1* to 6*. As others have pointed out, pulls aren't the primary pinch, here. Three- and four-star operators are sufficient for a large chunk of the game, during which you have plenty of opportunities to find 5- and 6-star units (you're guaranteed to get a 5+ in your first ten pulls from each banner, which is doable free-to-play). If you desperately want one specific Operator, you're in trouble, but you can clear most content working with whatever you find. The one- to- three-star units even have niche uses late in the game, given their very cheap deploy costs and their particular skills.
Stamina: Yuuup. It's called "Sanity" here, and it's notoriously stingy. Sanity recovery potions are few and far between, it's a long time between level-ups to expand your meter, and a single operation might cost you between a quarter and a third of your gauge, especially if it's got valuable drops. They're absolutely trying to get you to spend the premium currency "Originium" to reload...
Widget-based advancement: oh god, definitely. To develop an Operator to their fullest, you need LMD ("Lungmen Dollars", the plentiful gold-like currency), Battle Records, and a variety of weird materials like Polyester, Manganese Ore, Sugar... You're going to be strapped for all of them, at various points in a character's career. They can all be farmed, slooooowly, or you can get a stack of LMD and Battle Records with a weekly $10 "growth pack". The materials' monetization is more sneaky--you can't usually buy them straight up. Either you buy Originium to do extended farming, or you buy pulls. The credits you get for pulling duplicate Operators can be exchanged for many of the more annoying-to-acquire mats.
First hit free: Sure. Early stages go quickly, each one giving a dribble of Originium if you play half-decently; Sanity level-ups come every few operations; pulls from the newbie banner are generous. All these flows taper off after a few chapters.
Limited-time events: Arknights' events seem to be fewer and more involved vs. other gachas. There's typically only two banners active at any given time, and at most one big event with its own playable levels, currencies, rewards, and game modes. Lorehounds can find some of the juiciest story development in event plotlines, and each introduces new Operators and cosmetic skins.
Horniness: It's there, but a lot more mellow than e.g. Azur Lane. The character designers have a thing for bare thighs, but most of your base skins look more badass than sexualized. It's a mix of realistic street wear, tactical combat gear, and a modern or futuristic twist on fantasy spellcaster robes and cloaks. Premium skins are much more likely to be cheesecakey, but even there it's swimwear and the like, with exaggerated suggestive poses being more the exception than the rule.
Interior decoration: yup! You have four Dormitories in your base, which you can deck out in all manner of furniture and paraphrenalia. Even if you don't care about the look of the thing, you're encouraged to at least collect furniture and cram it in there, as the dorms' "Ambience" stat pays out in various ways across otherwise-unrelated game mechanics.
Whaargarbl UI: ...no! I find the UI really cleanly designed, and it's not all dropped on your head right at install. With relatively few active banners and events, you're seldom tapping through more than one intervening screen to get where you need to go.
Overall I've been impressed with this one. The monetization choke points are obnoxious, as is always the case for the genre. The gameplay, though, is some of the most engaging I've seen; the characters have a ton of personality; getting somebody promoted to the top tier, "Elite 2", feels reallly good.
For those who also play, my current standard squad:
Casters: Ceobe, Gitano (E2, S2M3 -- I later read that most 4* Operators aren't worth maxing out, but too late now! Still, she's holding her own as far as I've gotten)
Defenders: Saria (E2), Cuora
Guard: Lappland (E2)
Medics: Ptilopsis (E2, S2M1), Shining
Snipers: Exusiai (E2), Meteorite
Vanguards: Texas, Siege
Supporter: Istina
Istina, Gitano, and Meteorite are the most common swap-outs if I need something different in a given mission, in roughly that order of frequency. I'm getting close to E2 for Ceobe; Cuora's probably next up.