I played this game for the first time yesterday, and I LOVE it. It's not as complicated as it initially looks, and my 12 year old and I were able to figure it out after just one practice game.
It's not a game of total domination, so if you're like me and suck at RISK, you can still win at this game. Conquests are important, but the type of conquest is what matters most. In the final round, you can have very few territories but plenty of victory points.
You play by selecting one of 6 randomly combined race/power combos, then proceed on your turn to take as many regions as you feel will give you the most points. 6 regions will give 6 points, but 3 regions that complement your race/power combo could give up to 9 points, making domination less crucial than other games of this type. You can then choose to continue playing your race or put them into decline and select a new race to try.
There are plenty of websites that give a more thorough description, so I won't go into too much detail. A quick Google search will also reveal several videos of game play, my favourite being Wil Wheaton's Tabletop demo.
This game is easy to learn, fun, family-friendly, skill-balanced and lasts about an hour with 2-3 people. (You can have up to 5 players, or 10 if you combine Small World: Underground)