For a game to have a gameplay status for you does it have to be sandbox? It is a must for me, it immediately gives me the sense of the game actually being a game.
Yeah, I mostly agree! The sandbox stuff is kind of what appeals to me about non-traditional computer games and interactive fiction in general, that sense of having a world to explore outside the constraints of reality or a preset narrative.
Bonus points if the game has stuff to do that
isn't directly related to the nsfw content. Like, it feels more immersive and less like reading a visual novel if there's down time and mundane activities like going to school, working, shopping, or hanging out with other characters. Degrees of Lewdity (DoL) is probably the most successful example of this, but a lot of the big ero RPGs include life sim elements to some extent (TiTs, for instance).
Also, I just like seeing the worlds in lewd sandbox games. Since they're usually made by hobbyists/amateur devs, it's like viewing a raw slice of someone's mind, and there's often a strong sense of place that meshes weirdly with the lewdness. Like, DoL gives a pretty vivid impression of an English seaside town... overwhelmed by sex-crazed maniacs. Or take a more obscure game like ikkabod's Old School Blazin', with its 90s vibes and strangely unpleasant domination/submission mechanics. There's a disonance between place and content that I find surreal and darkly compelling in the case of DoL, and goofy but fascinating in the case of Old School Blazin'. Obviously, not all lewd sandboxes are that interesting, but the ones that are leave a powerful impression.
Anything with NPC schedules is also a plus. I like watching them going about their little routines.
At the same time, I also think not everything has to be a sandbox in order to have good gameplay. Some examples:
1. Lewd platformers and shooters tend not to have much in the way of sandbox-y mechanics, but some definitely have good gameplay. Others, like the old run-N-wape genre, are more of a grey area, in my opinion, where the porn is just kind of tacked on akwardly to the gameplay. Some even have a literal divide between the game and the pin-ups in an unlockable gallery.
2. I'm not sure whether certain types of lewd management games like slave trainers, card battlers, and strategy/tactics games qualify as sandboxes or not. Would you count them as sandbox games? They're often non-linear, and some grand strategy games (like eroTohoK, or XXXivilization) definitely have sandbox elements, but in other cases (like Portals of Phereon), most of the depth is in the combat/tactics, not sandbox/life sim stuff. And some of the old school slave trainers are more like VNs with preset plots underneath a thin veneer of management mini-games.
3. Adventure games (like Treasure of Nadia, or grubby old classics like the Frank's Adventure series) are another grey area between linear games and sandbox games. I like 'em, but they're not sandboxes in the conventional sense.
I'd also argue that not all sandboxes are created equal. There's a lot hiding under that label. Personally, I find stuff like DoL and TiTs much more interesting than any of Rockstar or Bethesda's sandboxes, where there's a lot to do but not much freedom of choice in how you go about it. Something like Red Dead is satisfying in its own way, but actually feels less immersive to me than lewd life sims with pixel art like DoL, where the stakes are higher and the world (on the surface) more mundane.
It's like the difference between picking from a long menu of numerous but very similar options, compared to a short menu of a few very different options. More choices does not always mean more meaningful choices.
TLDR: sandboxes are fun, and they're one of the main reasons I like playing amatuer lewd games (and especially, exploring the weird worlds that hobbyist devs create). But what consistutes a sandbox game is kind of hard to define, in my opinion.