I believe its not decades of playing, or knowing every rule / game that makes people enjoy these games. It's the chance to be other places, see wild things, and probably almost die in all sorts of wild ways while maybe looking awesome or smoozing past warlords. I believe in the rule of cool, as in if it's damn entertaining its a lot more likely to work. Or at least if it doesn't work, there will be applause at the funeral. I tend to cuss a bit (years of being surrounded by military will do that). I think the most important thing in putting a game together is how a group gels. A good group or GM can make any game great, while jackasses can ruin a game no matter how fun it sounds. I mostly stick to 5th edition D&D and FFG's Star Wars these days but am pretty open to anything.
An unfortunately necessary note: Yeah, I am a trans woman, whoopy. It's a big ball of fun and sunshine. And has jack-shit to do with gaming. No, It's not exciting, or interesting. It's not a big deal to me, so hopefully it isn't for you. Again, this note has been made necessary by the usual shitty people out there. All games I run are LGBTQA friendly. Which means open to anyone who can be an adult and just have fun. Friendly doesn't mean defined by, or even about these folks or themes, it just means we can game without trolls making boring comments. (Because trust me I have heard it all) And thats pretty darn rare sometimes. :P
Also: Been known to make ridiculous sound effects while DM'ing. It's a sad sad thing. Or an awesome thing. :) ZOOOM vreeoooom. BOOM. Etc. :)