Within my particular niche interests, I would say...
-'Twink/Bearworld': Gay M/M games fall into two camps with regard to body types, or three if you count Yaoi-inspired ones. Everyone is either a twunk/muscle queen fresh from a fully body waxing, or a parade of stocky, hairy rugby players, and never the two shall meet. I'm just so tired of it. And let the little guy top, please.
-'The Gay Furry Game': Not exactly a trope, but more of a trend. It seems, on the M/M scene, the only people willing to fund games are obscenely rich furries, so I would guess you have a 70% chance of any gay game being exclusively for, by and about furries. Now, I love me some scaly boys (or bug people, but I never see those!), but it's always lions/tigers/bears and I think of the fur down there getting matted with juices, and I just... dry heave D: Sorry, not for me.
-'The UnPorn Game': You find a game project that looks promising, and after downloading it and playing it for a little, you discover that for, say, an RPGM title the gameplay is very respectable. There's some genuine challenge, like an old school rpg, and you get the feeling that whoever made it was quite capable at game design. Even the porn CGs/Animations seemed at least competently made before downloading... until you get to them ingame, and discover that nothing about the porn element was as advertized. There's no description. No dialogue. If it's a battle fuck game, the grapple/stance system will be bugged, broken or completely nonexistent. Scenes will show wonderful art... and be over in seconds, with prose that would have the author of Thomas the Tank Engine asking for a little more complexity. Yes, I'm talking about you, Rule of Succubus.
-'The Battle of the Sexes': Something I see a reasonable amount of, but usually in Japanese porn games, is some kind of fantastical or mundane excuse to pit girls against boys, and while it's sometimes handled okay, what it usually acts as is a vehicle for sexism and biological essentialism. As I'm quite fond of femdom games, this means stroking the presumed male audience off under the table, reassuring them that women really are weaker and need to 'trick' them into sex in order to win. It's like they can't quite bring themselves to go full Tower of Trample 'women are superior' in case the men in the audience start screaming, so they instead constantly bring up tired, sexist tropes surrounding what I can only assume the author refers to as Duplicitous Feeeemales.
-'Top = Dom', or 'Penetration is Power': This is one I see everywhere. BDSM people do it. Vanilla people do it. Gays and straights alike do it. So, of course, porn games do it too. Closely related to the the idea that Penis = Power. Guys, just because someone is being penetrated doesn't mean that they have to be the submissive one in the scene. The power dynamic can go any which way. The guy bottoming could literally be holding the guy topping's leash and people would assume that the top is the one calling all the shots, I swear. I'm pretty sure the idea that women are inherently submissive shares common ancestry with this trope. Please, god, just let people powerbottom on occasion, or have a woman blackmail the MC into fucking them for a change.
Oh, and I just wanted to take a minute to defend Game Over Sex, because everyone I see talking about it seems to hate it. I feel like some players, and probably a fair number of devs copying the monster girl trend, have rather missed the point. In a game featuring battle fuck mechanics, or some kind of temptation/seduction combat elements, the conceit of combat is that the main character kind of wants to lose. The enemy is specifically trying to tempt and/or force them into doing so. That's the entire point of the encounter, usually, unless the designer missed the memo too. Ideally, that diegetic (in-universe) desire that the MC grapples with is the same one that the player is grappling with to not just hit the 'wait' button, or stop struggling, and that shared sense of anticipation is what makes the dynamic hot.
Combine that with looking at the design of your opponent and thinking 'wow, I wonder what they'd do to me?' and listening to them describe what they want to do to the MC, and it's a character conflict I find really sexy. Then you let them do it (or put up token resistance), find out what happens, (hopefully) get off, and then retry the fight to do it properly this time. The themes of the combat, seduction/temptation, align with the player's incentives in combat. They don't want to lose, because losing would set them back five minutes (or for the MC, bring ruin to the world, etc) but both are grappling with the same 'it would be really hot to give in tho' problem, and that's actually really good design.
Obviously, if you aren't interested in being dominated, or in watching a cute, wholesome guy get used as a fleshy dildo (that's me btw), then this mechanic is probably going to get you very, very mad, and that's fine. People can like what they want. But I do kinda feel like people have missed the thing that makes game over sex/rape sexy, at least for me.