Two more fun non-D&D games:
Dogs in the Vineyard
You play a group of armed teenagers with a mission from God. You visit various towns where the Faithful live to straighten their ways and help them solve their problems. It may seem simple at the beginning - after all, you have training, you have guns and you have the book full of holy texts...
But the conflicts you encounter are never black and white. There is rarely a person free of fault, and rarely a person who has no good reason for their sins. You know the religious law, but it doesn't mean the law is always fair. And neither the God nor the GM will tell you what the right choice is.
Whose fault it is? Who should step back here? How far you'll go to get things your way? It's up to you and you only.
The basic resolution system is the same in each type of conflict: you roll a pool of dice (based on your stats, traits, equipment and relations), then spend them to "raise" (perform actions) and "see" (block opponent's actions), until somebody backs off or runs out of dice.
Strengths:
- Elegance and thematic focus. The game is very clear on how it is designed to be played - and what it aims to do, it does very well.
- The system really supports the playstyle. The escalation mechanics (you can continue a conflict instead of being defeated if you decide to use more violence: talking->grabbing->beating->shooting) forces one to think how important is what they want to do - how much they're going to risk and how bad they're ready to hurt others. Consequences of a conflict are rolled when it ends, so one never knows how badly they are really hurt - only how much they risk.
- Very clear GM guidelines for designing towns (adventures - or rather just problematic situations that PCs interact with). It's really hard to make a bad adventure while following them.
- Rules are simple; it's possible to create characters and start playing in 5-10 minutes if GM has a town ready.
- The setting description has little details. It contains everything that's necessary for the intended playstyle, and leaves most of the color in hands of the group.
Weaknesses:
- Narrow. The game beautifully supports one style of play, but only one. It may easily be refluffed for a different setting (I've seen, for example, Jedi in Star Wars), but id does not fit different playstyles.
- The system is explicitly non-simulationist (there is an example in the book of giving low dice to a trait indicating high competence or vice versa - "I'm really good at shooting, but it creates more trouble than it solves"). This may turn some players off.
Nobilis
You play godlike beings, each of them controlling an aspect of reality (like cars, anger or deadlines). You are ruled by an evil tyrant and brilliant strategist, who outlawed love and who's destined to save the world unless he betrays it. And you are at war with Excrucians, beautiful beings born of nothingness, who want not just to destroy our world, but to prove it's so nonsensical that it could never have existed.
The resolution mechanics use no randomizer, only resource allocation. When actions come in conflict, both sides spend points to improve their skills or miracles, and the highest result wins. You can play tactically by not trying to overpower your opponent, but instead letting their action succeed in a way that benefits you more.
The rules are not metagame; one can see the decisions taken in play as their character's. But the rules the Nobles (PCs and other beings of their status) play by are very different than those of our world. Conflicts sometimes look like philosophical debates, with characters' powers redefining beings and ideas, making metaphors real and real things metaphorical. It can be extremely fun - or extremely confusing, sometimes at the same time.
Strengths:
- The game handles extremely powerful characters without any balance problems. Pure numbers mean much less than how you use them - and every character can do things of epic scale.
- Reality is text, or game, or computer program, or something even stranger. A lot of fun comes from approaching problems from a perspective that's completely different from real life or more typical RPGs.
- It's easy to be defeated in a conflict, but very hard to permanently lose your character. For many PCs, being dead is only a minor inconvenience - and for some it's a state in which they begin play!
- The type of powers the characters usually have really reward creativity and flexible thinking. It's as far from "list of powers and a battle grid" as possible.
- The setting is fascinating - especially the Excrucians. And where it's not detailed, you know what style to follow when filling the blanks.
- You get special tools for character creation, that help people with already existing character concepts detail them and make them multi-dimensional, and people who don't have any concept yet to come out with an interesting one.
- The system has specific rules for long-term and wide-scale projects that, on one hand, ensure that players can achieve their goals and are not dependent on GM fiat, and on the other hand, make the way that leads there interesting. That's the best game I know for this kind of activities.
Weaknesses:
- The rulebook is very nice to read, but hard to use when you just need a specific piece of mechanics. You absolutely need to read the entire thing once or twice before game to have any chance of using it.
- You can and will be surprised a lot, on every session, no matter if you're a player or a GM. For me, it's fun, but some players don't like the feeling that they have nothing constant, solid and safe to rely on.
- Each character will change, a lot, in ways the player can't control. If someone doesn't like social mechanics that dictate some aspects behavior, Nobilis is not for them. While it is possible to shield a character from externally-forced changes, it is neither interesting (doesn't lead to an interesting story) nor tactically efficient (requires spending a lot of miracle points on things you otherwise wouldn't have to).
- The game is strange. Not "quite strange". It's strange on the "Alice in the Wonderland meets Matrix" level, or somewhat more. You either enjoy it, or run away screaming.
