First of all, Settlers is the best board game ever. I devoted a thread to this topic a few months ago.
Second, thanks to Joker for pointing me here.
Third, go
here to play Settlers online against real people. For free.
Now to your questions, Patrick.
It's easy to learn.
It's easy to teach.
It's a great game to play with in-laws. I play with the mother of a good friend of mine, my friend's 15-year-old brother, and a varying fourth player about once a week. And sometimes my friend actually plays, too. [img]/images/graemlins/smile.gif[/img]
The game has a nice balance of luck and skill. A first-time player can win, but a long-time skillful player is more likely to win.
Collusion is quite possible but not to be feared. While it's certainly true that two or three people can gang up on one player, that strategy quickly goes down the tubes when the victim decides to exclusively help one other player. Just make sure you pick the same "ally" every game. Pretty soon, the other two players will stop colluding with the third player because they'll realize that, in thwarting you, they're only helping the other guy to win. It's a remarkably effective counter-strategy if you plan on playing with the same people over and over.
If your opponents are quite tough and become good at the game, introduce Cities and Knights (an expansion). It adds many layers to the game. Basically, C&K reduces the impact of trading and favors the players who are able to make the best use of many options.
Seafarers sucks as its own expansion. Seafarers with C&K and the original game is pure ambrosia.
For the original game, a dominant strategy usually becomes apparent for each game. But such a strategy varies from game to game due to the randomness of the board, and a dominant strategy for one player is almost never the same strategy for another player in the same game.
Aieee! Settlers rocks. If you'd like to chat more about it, PM me. I'm always excited to talk shop about this game.
I recently bought all three games for under $80 total. I can dig up the website if you're interested.