Pros and Cons of The Window

I have never used a system or watched someone else use a system that is better than the Window. It is simple, flexible, and, most importantly, completely free. The rules to the Window can be found at http://www.mimgames.com/window/. There is talk amongst roleplayers that the Window should not be used by beginners, but such a beautiful system should be what roleplayers interested in storytelling use first.

Strengths of the Window:

• It is an incredibly simple system. Each ability that a character possesses has a corresponding die. When you need to use that ability, you simply roll the die and see if you get a 6 or lower. That’s it.
• You do not have to limit your characters to archetypes. There are no pre-determined character classes. As long as the Storyteller (Game Master, i.e. the person running the game) agrees, an Actor (Player) can make a character with whatever combination of abilities that she wants and she can be just as good or as bad at those abilities as she desires. It is difficult, though not impossible, to play a suave and cunning orc rogue in Dungeons and Dragons. It is incredibly easy in the Window. 
• The Window does not pit the Game Master against the Players. Everyone is working towards the same goal — making a good story.
• It is totally free. All of the rules for and theory behind the Window are online. There are no books to buy.
• All you need are dice and an imagination. Also some paper. Paper helps.

Difficulties of the Window:

• You have to make everything yourself. Before our first session, both the players and I had to go through a lot of preparation. 
• The Window is not as good for people interested solely in “winning.” If all you want is time to zone out and fight some monsters with your friends, then a d20 system might be better.

Play Styles: Winning and Storytelling

In my experience, there are two paradigms of play, two reasons for playing. Both of them will always be true to some extent, but one is usually more important to an individual than the other.

Winning

These players want their characters to come up against and beat increasingly difficult challenges. Mostly, this means fighting monsters, but it can include solving puzzles, persuading NPCs, and whatever else you as a GM can think up. For people with a focus on winning, the plot is mostly a way to get them to the next challenge. Their characters are often (though by no means always) fairly static — their personalities don’t change that much over time.  During character creation, their focus is on how to make the most powerful character they can.

Storytelling

These players are interested in collectively telling a good story along with the other players and the GM. Plot and character development are much more important for them. The characters they make will often come with built-in flaws, which the player will want to exploit at the character’s expense. Players interested in storytelling will kind of want their characters to fail from time to time, since this is more compelling narratively. During character creation, their focus is on how to make the most interesting character they can. 

Both of these play styles are totally legit, and it's more of a continuum than an either/or situation. But in my experience, each player is going to lean more towards one style or the other, and each campaign is also going to lean one way or the other. Ideally, the GM and all of the players will be more interested in either winning or storytelling. During the beginnings of my current campaign, I had a player, Panda, who who never seemed that into what we were doing. He was always reluctant to jump into scenes, though he continued to come every week and listen intently. I did several things to try to bring him more into the roleplay. I often asked him what his character would do; I gave him a special ability; I even let him make another character. Yet he remained on the sidelines. It was not until later, after he had left the roleplay that I realized what the problem was. The rest of us were interested in storytelling. He preferred the winning style.

It is almost inevitable, however, that play styles are going to clash. Even if every one of your players is interested in only one of these two broad categories (and it's almost certain that they won't be), people will have different play styles in some other sense. One of my players, Hamster, loves the more adventurous elements of our roleplay. When we haven't done anything exciting for a while, she'll say, "Come on, let's get to the plot." But Puppy, another player, loves character interactions. I think he would be okay if the whole roleplay was a high school soap opera. So, as a GM I have to find a good mix between those things.

Basically, to sum it all up: make sure that every time you play, there's something for every player to enjoy.