I thought about this for awhile and damn, there's a lot of genres I wish I was better at. x)
RTS games just overwhelm me way too much. I am (or was) pretty good at Homeworld, not the worst at Company of Heroes or the Dawn of War games and that's about it. There are so many really neat ones, like World in Conflict, that I wish I could handle but I just can't.
I have never been very good at Fighting Games either. I can usually do better than most of my friends in games like Soulcalibur, Bloody Roar, Dead or Alive and Marvel vs. Capcom, but I have been humbled very quickly if I'm feeling spicy and try to play online, or with a couple of buds who do know their stuff. I button mash too much, I switch characters constantly so I never get good with anyone, my reaction time isn't great and remembering inputs is just too much for me, it's all super overwhelming. However, I am pretty good in games like Nidhogg, Bushido Blade and other similar games. I can also hold my own in, uh, I guess you'd call them party fighting games? Like Power Stone and Gang Beasts and other such things. I used to be rather solid at Smash, but my skill has atrophied significantly. I don't know what subgenre the Ultimate Ninja STORM games are, but I actually crushed people rather often in online matches, if anyone knows any games like those lemme know. In the end, I'd sell my soul if I could play any fighting games at a competitve level, especially games like Street Fighter III: 3rd Strike, Killer Instinct (2013), BlazBlue (Okay, I only want to play as Jubei.) and Tekken, as well as many more. Watching online matches with good players is hype as fuck.
I don't know exactly what genre it's considered, but Dwarf Fortress and games like it, such as Rimworld, Space Station 13, Kenshi and many others. They overwhelm the fuck out of me (See a pattern here?) and I just have a huge aversion to most sandbox and procedurily generated games. I wish I didn't, because I know they are pretty much an infinite good time, but I can't force myself to enjoy something that I don't enjoy playing. I could listen to player stories from these types of games forever, they can get really nuts and hillarious.
Next up is FPS games. Of all the genres I could mention, this is the one I'm best at. I used to slay in Left 4 Dead, I was okay in Team Fortress, Battlefield, Call of Duty, Payday 2, Overwatch and some others. I've beaten many FPS campaigns too. However, I can't handle really old and clunky FPS games like System Shock 1, really hard ones like Blood and especially really fast ones like Ultrakill. Why? You should know by now! I get overwhelmed! Not much else to say, it just sucks that I can't handle certain games.
Stealth games come to mind too. Metal Gear Solid is probably what lots of people immediately think of, but those games, while awesome, aren't really super stealthy. The Hitman games are much more stealthy, but with the amount of ways you can approach stuff, they don't feel so bad. What I'm talking about is stuff like Alien: Isolation, Thief, Commandos, Dishonored and others. Yes, yes, they get overwhelming too. Keeping track of guard's routes and doing stuff sneakily and using the environment to your advantage all at once just does not click in my brain.
Rhythm games in general. I was able to beat all the songs on Guitar Hero 1&2 on the standard difficulty and I got to the last level of Um Jammer Lammy and that's about it. x) I need to try Hi-Fi Rush and BPM: Bullets Per Minute to see if I can handle them. I doubt it though.
Shoot 'em ups, either side-scrolling or top-down. Ideally side-scrolling. I've only beaten Gunstar Heroes, no other shoot 'em ups. D: There are so many awesome looking ones, both classic and modern.
Text and graphic adventure games. Not much to say, I just don't have the patience to try a million different words and their permutations and combinations. I know they've gotten better with time but pixel hunting and softlocks and instant deaths aren't my bag. I really want to love those kinds of games, I've tried them many times but bounced off them each time.
Roguelikes, but not how they are widely known today. More in the style of NetHack and such. I quite like modern day roguelikes, but I've never been able to enjoy the classic style.
First-person party-based dungeon crawlers seem pretty neat too. I have gotten into a few and played them for a good chunk, but never finished one. I don't know what it is, they just kinda lose me after awhile, can't put a finger on why.
Finally, city building and adjacent games, like Cities: Skylines, SimCity, Surviving Mars and so on. I just don't have the foresight and planning ability to make anything terribly successful. D:
...Man, I wrote a lot of words. I can play some games, I swear! I wish all these were amongst them though. They all appeal to me in different ways and I wish I could get the same enjoyment out of them that many people do.