Heroic deeds of daring-do. Getting to be awesome, do awesome things, and have fun doing it. If I'm playing in a setting which is ripe for exciting adventures, action, and battles to be fought... let me fight them and not agonise constantly over doing it, or punish my characters for doing what they're there to do. I play RP's to get outside of my normal day-to-day life, not get lumped with more consequences. 
Although, internal consistency is key to making a good RPG. Does the world make sense? Does whatever magical/technological phlebotinum that's been conjured up to make the setting work have rules? 
I love a good setting and plot for an RPG. That's what will draw me in. 
I'm not at all a fan of slice-of-life games, and I [b]hate[/b] school RPGs. Seriously, the amount of those goddamn things that come up is probably why I don't participate in more games, and so many good ideas have put me off by being *thing you really want to do*-school.

Definitely prefer a tone that's serious for the most part, but can have moments of darkness and moments of humour alike; kind of like the MCU in tone really. Never really been able to get into comedic RP's and anything too grimdork just gets too much of a slog. 
Genres, I love sci-fi, especially mecha sci-fi. But I often see games that are based on fandoms or video games that are just... meh. Or go down the boring tournament fighting route, or try and make it some weird neo-fantasy thing. Or again, too focused on realism (despite the fact they're, you know, giant robots).
Military games can be fun, but are often too po-faced, or too focused on shiny toys or Call-of-Duty style stuff, or too much 'gritty' realism to be any actual fun. 
I'd love to get into a good fighter jet RPG, but all the ones I've either run or played in have died off. But tbh, that's the same for most RPs lately, they just die before they get anywhere.