My Four
1.) What's the ref style (Hard Sci Fi, Soft, Goofy, By the book, Loose rules)
I've seen some games run nearly without dice and others devolve into two hour discussions on theories of quantum physics to decide whether a character's actions worked or not.
2.) What game style (Diplomacy/Social, Action smash and grab, Trading/Money, Moral Dilemas, Exploration, Political intrigue)
I've seen some games with way too much action.. some with way too little, and too much talking... some games where its hard times and you have no money.. showing up to a 1,000 rounds gun fight with 50 rounds.. those are fun... some games where money is too easy and the players own gigantic corporations.
3.) Definitely frequency and duration of play!
Make sure you can actually show up on the schedule... twice a week for five hour sessions... maybe when i was in college I could do that.
4.) Have the other players already started, and how long ago
Personally, I hate walking into a game as the newbie with newbie skills and everyone else is maxed out on skills, equipment, and cash... makes me feel rather useless and usually is a waste of time to be there. Better to start all near the same time and be similar.
5.) One more thing... do you get to generate your own characters? One time the ref handed us pregen characters.. just didn't seem as fun to me.
For me, I don't worry about rules and setting so much. That's the ref's job and I figure they should be able to choose what they want and are comfortable with. I can always learn the setting and rules as we go if they're different than what I know.