For a game that is undoubtedly most fun to play with 2 other friends, it seems like the multiplayer was an afterthought in some ways. Such as;

1. Achievements only being unlocked for the host, meaning if you want to convince your friends to do a challenging run to get an achievement such as "Reach the reactor without the crystal taking any damage", you'll have to do it on all 3 of your saves.
Proposed Solution: Simply unlocking the achievements for the guests as well, perhaps I'm ignorant to some technical limitation but surely that's trivial right?

2. Weapon upgrades based off of the hosts progression, a vector of expression and control over your own build being delegated to "Hey bro can you spend your points upgrading the guns I like?" I've heard people say that that's intentional so your friends can't come in with overpowered weapons and carry you, but from my experience none of us would really care, we just want more expressive and personalized metaprogression.
Proposed Solution: Either allow gun progression to be player based, or perhaps offer other types of metaprogression that allow someone to really spec into a build they enjoy.

3. In order to manage your hero chips while in a multiplayer session you have to exit to the main menu, load into your own saloon, do the modifications, then rejoin your friend's lobby.
Proposed Solution: Can't think of any reason to not just let people manage their own armory in a session.

Gripes aside, we have been having so much fun playing coop together and are really excited for what's to come with the game, cheers on the release :D

My friend never complained about having to quit lobby to equip their Hero Chips, so I would assume that is a bug and isn't a design error.

At least we had zero issues so far on Hero Upgrading Separately in 10 hours of Coop.

Upvote

Sadly crashing seems to reset all progress for guests, we finished a run to completion but had a crash in the final room so when we finished guests got no cells and hardly any scrap but host got full score and rewards. My quest on Shroom also completed but I didn't receive the beverage needed for the next step so I'm not sure if it's softlocked out of progressing now. Might stick to single player for now unless I'm trying to catch friends up by running with them.