It's a fine DLC. Outlined below are my thoughts on the campaigns as a whole. I won't be talking extensively about the stories/lore of each campaign; there are plenty of video essays on the topic already.

A huge mistake going into this DLC is expecting the same experience the base game brought you -- as many reviewers have already mentioned, you will be sorely disappointed. I initially wasn't going to review Downpour for this reason, but I saw a review of Rain World that mentioned how the DLC ruins the original's tone and narrative, citing the DLC's new technical features and story as the culprit. It got me thinking: does a game owe its audience an expected experience at the cost of ingenuity?

I don't think so, at least not to the extent that Downpour "changes" the original. It's best to view each campaign as a separate experience that is part of a greater whole, instead of thinking of each campaign as an extension of the previous one.

Downpour gamifies many aspects of the original in a way that makes it distinctly clear that it was originally a fangame created by multiple people. I personally don't find this as offensive as others might, especially with how each story utilizes its differences, but you may be turned off by it if you were expecting just more Rain World. Some campaigns may be a fetch-quest, some may be more story-oriented, and some may lie somewhere in between. You're still a slugcat that has to survive in a world that is completely indifferent to you. The only difference between campaigns is how they choose to present this idea.

That isn't to say that Downpour doesn't have its problems. A lot of the new creatures feel like unnecessary addons, and some of the new slugcats' mechanics can feel very under-utilized. There are areas in the DLC that made me want to pull out my teeth (if you know, you know).

The continuation of the story/lore is also a mixed bag; in some campaigns it's told incredibly well, while in others it feels like the developers were trying to tell more than they conceivably could.

In any case, I don't think any of the differences present in Downpour damper the quality of the original. Yes, Downpour isn't Rain World -- but it doesn't try to be, and that's perfectly okay.