What I saw was people mostly complaining about two things in the game:
1- The “mana” system. A complaint I don’t agree with, but whatever.
2- The lack of “flavour” of the game. Basically it feeling too dry and not period specific enough. This I agreed wholeheartedly (I preordered and I will buy the DLCs, since I think there’s alot of potential there, but after one full campaign I’m unwilling to play for a year or so until the coming changes are implemented).
Then yes, you have people bringing up the DLC issue. Sometimes on its own, but sometimes related to point 2 above. But the bulk of the criticism I read had many hours of playtime and addressed specific concerns with the game vs. other Paradox games. I mean, I could certainly have been fed specific reviews versus others, but I did not get the impression of a review bombing.
And the graph @Telefrog linked to rules out any review bombing, with very, very stable positive/negative ratios over the game’s lifetime. I’ve been watching the reviews, and the ratio has dropped from an initial 70+% to the current 37%, so if anything there was an initial “positive” review bomb when people did (on average) have less playtime than now that has steadly move over more negative reviews (recent reviews are at 25% positive, and there are 400+, so it’s a significant number).