Catan is an excellent game. I would highly recommend it. I have introduced the game to about 8 people to date, and they all loved the game. While the box looks about as boring as dirt, its actually really fun.

It takes about 10-15 minutes to learn, and about 2 hours to complete a game. So I would say this meets your criteria. The game is for 3-4 players, but you can buy a 5-6 player expansion for pretty cheap.
After playing it, you will see that the game is very heavily based on trading goods and land property, which is why it is often compared to monopoly. The key difference is that Catan does these elements right. The people actually want and need to trade. There is also no such thing as owning the "best" property. A property that may seem good in the beginning of the game may not be so hot later in the game. The game is strategic, but does not require heavy thought like chess would. It requires more thought than a game of monopoly, because you have a choice in what you do.
The game also uses changeable hex tiles, so the dynamics change every game if you want to change the setup, you can just shuffle around the board.
A few warnings about this game though:
1) It is a gateway game. It has expansion sets and you will be tempted to buy them. You can enjoy the original game fully but the expansions do add some very cool elements to the game.
2) There is still dice luck involved. This is a big turn off to many people if the dice seem to play favorites. The nice thing is that even if the dice don't go your way, you can still turn the game around with shrewd trading or building.
You can play the base of Catan on their webpage for free if you want to try the game:
http://www.catan.com Click the "play" button on the left of the screen. There is also an online tutorial on the website as well.

EDIT: I just wanted to add that the base game can easily be played in 90 minutes, after everyone is used to the game, and if you don't have the tv going in the background like I do.