Hi, welcome to the forum.

The DLC are every bit as fun as the main game, you also get a few new powers and weapons. Daud is an interesting character, it was nice to learn more about him. Both parts have slightly different atmosphere - TKoD is more down-to-earth, 'a day in a Whaler's life' style while TBW gets more eerie and magical (you deal with conspiring witches, after all). The only thing I didn't like was how Arkane handled Daud's motivations and fate at the very end, but it didn't diminish my enjoyment of the DLC as a whole. I'd definitely recommend them.
One thing though, if you want to buy them it's best to wait a few days until Steam starts the winter sale.