Me? Personally? Two things. Unique story (as in, new take on old themes, strange premise, etcetera) and character customization. If I'm going to be spending 20 hours in your RPG or more, I like to be able to customize my characters to my particular needs and wants. I don't mind a general character and a general playstyle, but I like the option to tweak those things a bit. I like tweaking my equipment if at all possible as well (so long as there's plenty of variety for tweaking, instead of just a linear progression of tweaking. I prefer choosing what element my sword is over making my sword do 2 more damage in terms of tweaking). I like tweaking my Skills/Spells if possible as well. I also generally LOVE skill trees with EXCLUSIVE options (as in, if you pick this, you can't have this). Well, I prefer skill webs of that nature, but trees are fine too.
As for the "unique story". I just like to try to experience something new and interesting. It's how I decide what movies to watch, what TV series to watch, what books to read, what anime to watch, what board games to play, what video games to play, and sometimes even what food to eat. I like new experiences, or new takes on old experiences. "You play the villain" isn't enough for me. "You have been given $10,000,000 and can't spend it on yourself, but are given a phone that lets you buy goods or services immediately or later on down the line, with the expressed intent that you must spend that money to make the world a better place, how you see fit... But, you have competition, and someone has to win the game, so whomever doesn't actually succeed dies... Oh, and one of the competition is actually someone who takes care of people breaking the rules or causing mayhem, but you don't get to know who..." That... That I would play. In fact, it's an anime I've watched.
I like stories that break molds and defy cliches and tropes. I'd like a story like "You Are Not The Hero". It's a game I'd play if not for the "mini-game" like gameplay the game exudes. I'm not a fan of mini-games in RPGs (to the point that I wish they didn't exist), but the story of that game seems pretty fun and probably even interesting and entertaining to me.
First, I look for games that defy the ordinary in terms of story and plot. Then, I look to see what I can customize (if it even matters to me at that point... which if the premise is interesting enough, it might not). That's when you've sold me. If all your game consists of is "save the world from the big bad", then I'm just not going to be interested, unfortunately. If the game is "Who actually IS the big bad that we need to save the world from?". Well, that might be interesting enough for me to take a look.