Broken steel is an must buy for anyone that wasn't ready for fallout 3 to end, as it gives you and extra 10 levels to achieve (up to 30) and re-opens the fallout 3 map in all its glory. The basic premise is helping the brotherhood of steel wipe out the remaining Enclave, but you're free to wonder round the map as usual finishing off any unfinished quests or unexplored areas. And fighting alongside the Brotherhood of Steel with their ridiculous heavy weaponry is always entertaining.
Point lookout is an off map island covered in radioactive swapland and inbred hillbillys that you travel to by boat, and has its own array of charters and quests, much like the original fallout map on a smaller scale.
It is not easy, I wouldn't recommend having a crack at it until at least level 20. Be fully prepared for your favourite weapons not to be so effective out there, and you will have to adapt your playing style to deal with much tougher enemys in much greater numbers than before. I spent more time in "tactical retreats" in the first 30 minutes of playing Point lookout than i needed in the entire fallout game.
There are some fantastically realised and well thought out quests in this game. With the presence of some voodoo magic provided by local tribes people allowing the makers more room for artistic licence, the results are some pretty bizarre, funny and very dark stories. A very entertaining expansion pack, definitely worth the money. It is not a holiday destination though, be prepared to fight for your life.