The wacky humour continues. The heroes had a party and lost their portal controller, so you have to retrieve it. DLC is another campaign more of the same: the love story of the first chapter continues, the fourth wall gets utterly wrecked again and the difficulty of the levels is higher than in Chapter 1, but this is okay as you have assumed to have completed the first one anyway. You're still good to know your internet memes and pop culture.
New stuff are the Smithies, i.e. factories that produce machine units, and Monty the dragon has switched sides. You also get to control his spawns, drakes who are hilariously ambitious. As you are again going after the Arch-Lich, the story is very much the old one in new clothes, which is fine as it retains and enhances the humour on the way basing it on Chapter 1.
If you enjoyed the first campaign, i.e. Chapter 1, you'll probably enjoy Chapter 2 as well.