This game's blurb describes it well: smooch.click is an experimental kissing simulator. And it's focused on the moments that lead up to the kiss.
Gameplay is choice-based. I played through a handful of times. (The game is quite short, and so it invites multiple playthroughs.) During each playthrough you are presented with a few scenarios, most of which give you three options. After three or four (or maybe five) of these scenarios, there is a final scene featuring a kiss.
I got mostly different scenarios on each playthrough. Once I saw a scenario at the beginning that had appeared near the end of a different playthrough, though. So the scenarios must be (mostly?) randomly selected each time you play.
The way the kiss scene plays out appears to depend on your previous choices. When I tried more romantic choices I was generally rewarded with a more tender kiss scene. The one time I tried choices that were more indifferent or dismissive toward my date the final scene featured a "bad ending," with (Spoiler - click to show)a spider, me hitting my head, and a trip to the hospital.
The choices aren't presented to you in list form. Instead, they cycle through at the choice's location in the text, on a timer of some sort. I don't in general like text on timers like this, but in this case I think it works. It felt like it emphasized the split-second decision of some choices (if I don't click this now, I'm going to have to wait until it cycles through!), as well as the almost arbitrary nature that choosing sometimes has. Romantic situations where you're trying to feel out the other person particularly feature this. Sometimes "the moment" passes, and you're aware that you've missed something that you won't be able to get back. (However, in smooch.click, if you wait long enough, you will be able to get "the moment" back.)
The text doesn't feature capitalization, which can sometimes come across as an artificial affectation. But I think it fits here, with the work's experimental nature.
I find the choice of the word "smooch" in the title interesting. Why not kiss.click? "Smooch" feels a bit informal and a cozier word than "kiss." It's also somewhat like the sound you make when you kiss. "Kiss" is a more generic word and so feels more bland. So, yeah, I think smooch.click is a better choice than kiss.click.
The game's long list of content warnings made me think that this would be a much racier, darker game than it is (although maybe I missed those endings). In fact, based on what I saw, I would not put smooch.click anywhere near the erotica or adult interactive fiction categories. The choices that you're presented with are more about how you treat people in general or whether you are bored or uninterested or emotionally attracted to them.
Overall, this was an interesting experiment, but it felt slight to me. I think a lot more could have been done with potential story arcs.