Basically it's a stripped down version of the 4th Ed. mechanics, with all the errata thrown in. I like it so far. I still have yet to play (just DM), and we haven't started the Encounters Season yet.
If you see one in the store you should probably buy it. If nothing else, teach your kids or nephews how to play. It's literally as easy as teaching someone to play Monopoly. If you have a printer, download the pregen characters off WOTC's site and you're ready to roll.
I will post an update after the Keep on the Borderlands Encounter season starts. But, I'm looking forward to it.