Is all the dlc content interesting?
Depending on what interests you.
I would say that the four story DLCs (Dead Money, Honest Hearts, Old World Blues, and Lonesome Road) are very interesting and worth the money, with each one providing a different experience to the main game. They're also all connected in terms of narrative, so if you get one, you should definitely get them all.
Gun Runner's Arsenal is, IMO, also worth the money. However, it includes nothing but a bunch of new weapons (many of them really cool, like a blue flamethrower or a ballistic fist that plants a timebomb on every enemy it crit kills) and a bunch of new weapon challenges. No new quests or story. Just guns. And ammo. Most of it really awesome.
Courier's Stash is the only one I didn't buy, since it's basically just the four preorder packs bundled together. (Classic pack/Tribal pack/Caravan pack/Merc pack.)
Overall, I think that all of the NV DLC is assuredly worth the price they want. I bought it all at full price and I feel I've gotten my money's worth.