I bought it and played it a few weeks ago during a previous sale on steam this summer. Like you said, it was very cheap and even with all the negative feedback from everyone, I decided to buy it so I wouldn't regret it later when it's not available, I did hear the campaign was actually decent.
After playing it, I can say that I don't regret my purchase or my time spent on the game at all.
It's definitely not the best game ever, and I don't understand how Square Enix could believe this had enough content to be a service game, but the campaign was honestly totally decent / enjoyable. I don't know if it's that much of a compliment, but as a comparison and example, I think that Avengers in its current state is a better game than Gotham Knights for example.
The gameplay is really quite good, combats are fun, the different heroes offer some good variety, I think the game is definitely worth it just for the campaign.
The end game content is where it sucks. It's incredibly repetitive, it's always the same maps, the same objective, it's not really interesting, even in coop, so I would only recommend to do the main story and if you want more, the additional "dlc" campaigns, even if they are a lot more generic than the initial story (to be honest all missions that can be played in multiplayer share the exact same structure, you recognize them instantly, it's a shame, the best missions in the main story are the ones that are single player only).
Also something really important because it's way too rare, I think what Square Enix / Crystal Dynamics did to end this game is actually really good. When a game fail, most publishers would just decide to close the servers and that's it, making the game either uncomplete or even unplayable at all. Here they decided to remove ALL the microtransactions, everything is included, you get the full complete experience, and on top of that, I don't know how it is on console but on PC the game's online uses Steam directly, meaning it will still be playable online even after being delisted. We get a complete package with a still functionning online, that's really great for preservation and I wish more publishers would do this when they decide to close a game.
It's also worth noting that I say all of this as someone who hates grind, so if you're like me and just want some fun without going into heavy grind, it's still worth it.
My favorite character was Kate Bishop, I had a lot of fun playing as her and I didn't expect to enjoy it this much