If you plan on playing a catholic nation, in the HRE, or in europe in general, this DLC is kind of required. It added a lot of mechanics to the pope and other factions. Grumbling that some mods have added more content aside, if you want to play vanilla EU4 at its best, this is a DLC you should grab but wait for a sale. Or do the subscription thing.

We all kind of knew this game was going to not have as much depth in some areas as CK2. CK2 had almost a decade of support and some of the features, namely secret societies, are things that are blatantly missing from this game. However as of the royal court update that is yet to come out, it seems the depth that seemed missing from your character will now be there. At the very least this game is a good foundation for the future, a much better one than base CK2 was i might add. But that doesn't mean you should feel obligated to pay money to a game for the possibility of a good future. I think its worth a sale price as is. And the royal edition specifically i view as a great deal seeing as it will save you money as the first expansion and first 2 flavor packs are included.

If there is one major DLC you want to skip in stellaris its this one. That is not saying it isnt good, its just saying that it isnt particularly important to most playstyles. Megacorps themselves are not particularly engaging although some new updates have added some stuff. IF you really really want the features then its worth your money, otherwise grab it on sale and/or grab other major dlc's before this one.