It’s not random. It’s very much the same as a targeting doubled Battlecry (Brann Bronzebeard).

No, it’s always a 4 Drop. Watch the Video again.

We will see how much impact this expansion will have. But in average there are only 4-5 cards from every expansion inside a deck (30 cards/deck and 6 expansions + basic cards in Standard).
The main problem I see so far is, that this expansion has no key cards yet. Nothing you can realy build a deck around (Like the Quests, Malygos, Shudderwwock…)
But maybe we will see some later. “Dr. Boom, Mad Genius” and the Mechs are a good start.