I have played lots of different systems and in many different settings. I have also Game Mastered lots of different systems in many different settings. But what is it what makes a game good for me? I open some aspects here what those things are.
1. I like rules that are simple enough to run with minimum preparation but do also offer options for advanced gaming.
2. I like rules what are easy to strip to make them more simple if needed.
3. I like rules what are easy to modify and if there is no rule for something it is really easy to made up.
4. It doesn't matter if game uses only one type of die or all possible as long it is fun to roll the dice.
1. I like games where you see when character makes advancement. I like to see the difference instead of just next to no advancement or so slow or small advancement it doesn't make any difference.
2. There might be dozens of arch types or classes to choose from or only few but I like some customization to make my character my own not just a copy of book.
3. I don't like characters who get beaten up from peasants or die fighting rats and insects. I want my (and player's) character to be able to adventure and be a hero at the beginning, not after 10 gaming sessions preparing to be a hero. (Of course characters should be able to do more difficult deeds when they advance but I want to skip that beginning where your character is noob).
4. I also like games where I can make choices for my character build. Even if I start with one type of character I would like the option to make him something else during the game. It doesn't mean that my character should be good at everything, but I don't want my character to be tied in a certain build for the rest of the game (or his lifespan which ever comes first).
1. I like monsters scary. Even though they were easy to beat they should be intimidating. Look strange or scary, act strange or evil, be weird. Monsters should be something else than just next encounter to gain some experience.
2. I like simple but detailed monsters. It must be easy and fast to use a monster but still there should be something else than just roll a die to see does it harm player character. Easy to use but with some tactical benefices in combat.
3. Monsters should have something else to be there but only to be beaten for challenge. I want a reason why monster is what it is, why it does what it does and why is it there where it is. This can be covered in rules, or GM can write some reason for himself. If monsters just stand there at the dungeon waiting for player character it is a little stupid. Even a good background for the location might explain the monsters.
4. Defeating monsters should be fun.
1. Bad villains should be really bad. I like black and white oldschool setting in some campaigns a lot.
2. But still usually I want villains to be more in gray area. Are they that bad actually or is their agenda just twisted for the norm? Also villains who are not what player characters thought is fun.
3. Villains should have plans of their own. A life. They are not out there just to annoy player characters or grant questing for them. Villains should have more feel into them.
4. If you bring villain back later on game or in a different campaign do it once. That is enough. Unless the villain is not actually defeated or confronted majorly and campaign is about getting rid of what villain has done. But if the villain is main plot, I don't like that you have to defeat him several times (because GM likes him doesn't mean that players like him).
1. Static NPCs are boring. I want to feel that there are other things in the world than what player characters directly affect.
2. One to three features are nice touch to make unimportant NPC feel like a person. It doesn't take much time to tell that blacksmith has a black beard and strange sight but he is funny person. Without that blacksmith would just be a vending machine.
3. I want to have feelings for NPCs. To like someone, to be annoyed by someone, to feel pity and so on. Otherwise I just feel that my character is there alone or only with his group.
1. Short or long it should be interesting. What makes an adventure interesting is a harder thing to describe. It just is or isn't. If adventure is not interesting I hope GM will hear players' wishes how he could make it more fun to play (as a GM I also want to hear this from players to develop their experience).
2. Adventure should be somehow interesting for the character. Motivation why character would do it is a must. Otherwise it just feels like I created a tool to work things out in a game. I play my character and want my character also to experience the game. Otherwise I could play a board game or video game. "You are here and now you must do this" is boring without reason.
3. I like action but I also like social situations. Dangers and investigation are great. Even though campaign was combat focused I'd like to have something else there. Also even though campaign was drama focused I'd like some action or danger.
1. I am a big horror fan and would like games to include horror in a way or another. One night games might be hard for this if they are focused on one quest to be finished in a limited time but for longer adventures or campaigns horror theme is welcome. It doesn't mean I want zombies in every game, but some dread is always great.
2. I am open for different kinds of games from fantasy to science fiction but the theme should be interesting if the genre isn't my favorite.
3. Theme should also touch my character somehow. Otherwise it just feels that my character happens to be there adventuring.
4. I want to smell, taste, see, hear and feel the game. It is always great when Game Master spends effort to build up theme.
Those are some things I appreciate in roleplaying games.