I'm trying to remedy that now.
Both of them reward unique cards for defeating the bosses the first time. I really want those cards for deckbuilding since one of my goals was to get back into ranked play in Hearthstone. More cards means more options for ranked play.
The content is actually really fun. I don't know why I didn't stick with it the first time. Each boss offers a challenge that breaks the game in interesting ways. They have unique spells, minions, and hero abilities. It's been a ton of fun seeing what each one has to offer.
In a way, I wish the cards weren't locked behind a content wall but at the same time I truly am enjoying my time with the Solo Adventures.
If you're playing Hearthstone and haven't tried them yet I would suggest taking a look. You can buy the content one wing at a time, or buy the whole adventure in one purchase for a discount. There's a lot of fun stuff on offer.