Which of the DLCs are good

[urmom]

I read the reviews but wanted you guys' opinions before purchasing the game

[Biervampir [AUT]]

Heavily depends on what you are looking for.

- My Pet Dungeon
Relaxing Dungeon building with some puzzles

- Heart of Gold
Slower paced than the main campaign, but longer missions, exploration gets rewarded

- The Undergames
Selectable Difficulty, AI Skirmishes, with 4 different Underlords traits

[xepsubcn]

All are good, but the most I enjoy was Heart of Gold

[JVC]

My favourites were Heart of Gold and My Pet Dungeon

[Padelboot]

I definitely enjoyed the Heart of Gold campaign more than the regular one. Plus it adds the ability to turn units to gold (you can even make them decorative, which is a nice touch).
My pet dungeon also adds new units and the My Pet Dungeon mechanic from DK2, which I enjoyed a lot.
The Undergames... for those, who are into skirmishes with the AI, this is a very good choice. I wasn't as interested, but still got it.

Plus if you are interested in workshop maps and campaigns, it can be useful to have them all as people may place DLC units there.