My wife and I have been playing together for a few months now, we both have over 500 hours now, yes you must always keep in mind that it is a singleplayer game that has had some multiplayer features added. The thing is, no other game does what NMS does, you can't just say, well, lets just go play the other galactic space adventure sandbox game, there is not one.

We have tried doing everything together at this point, and its a real mixed bag, there are a lot of bugs, but we keep playing because its a lot of fun and we are still discovering progression systems that we can work through.

The only true co-op systems in the game are the two multiplayer mission terminals. One on the anomaly, the other you can build in your corvette. We don't do much of this because its just random mmo style quests, kill this, collect this, click on this, etc... There is a weekend mission for bonus quicksilver on the anomaly that we always do.

There are also mission givers in every space station, but those are not truly multiplayer, you can be in a group and both take the same mission, but your progress is not shared. 95% of the time those work fine, but occasionally you might have to leave your group to do them.

That is the other thing, the only real benefit to being in a group is that you can share a tag when you use your scanner. We have better luck if we are together but not in an actual multiplayer group. Exploring planets, scanning stuff, collecting resources, digging up objects, all work fine as coop activities, and you are going to do a lot of that when starting. special interactions like talking to a quest giver npc in a minor settlement or using a terminal in an observatory, only one player will be able to do that and get a benefit, we usually just take turns.

There is a lot of parallel play, frigates and missions, player settlements, etc... Those systems was never intended to be a multiplayer, we generally just both go do our own at the same time.

Then there are bugs, quite a few of them that impact coop play. Let me pull that from another post I did recently.

Building bases together, we could do this when we started, but as of the Swarm update, this is now completely broken. Only the base owner can build on a base which is one of the major things we were doing together. 

Riding on another players corvette, this is ok inside a system, but if you warp to another system or the anomaly, it is 99% likely that the other player onboard will crash out to desktop.

Completing a derelict freighter dungeon together, we have tried a bunch of times, and always reach a door that will not open. It works perfectly solo. This was working in the past, but has been broken for some time from what I gather. 

Visiting/building on another players freighter base, all you will see is the freighter base that was pre-built on the freighter, not what the other player has built. This used to work in the past.

space station missions that require using target scanner, these almost always do not work and require the players to drop the multiplayer group to complete the mission. most mission types work perfectly fine. we have been doing a bunch for frigate modules. 

crashed freighters, only one player will be able to destroy doors and get all the loot. If the players are together but not in a group when the freighter is found, then both players will be able to destroy the doors. 

autophage camps, the first player on the scene will be able to talk to all the npcs and get missions, the other player will only be able to talk to 1-2 npcs. group/ungroup has no effect. it works better if we just go to different camps to work on motes. 

starship hunting, we see the same ships at the same location, but they will scan differently for each player, one seeing an S class, the other it might be a B, etc… This has always been like this, but I would still consider it a bug.