So are ALL of the DLC’s bad?

Stellaris was broken for many many years and the DLC didn't fix the game. People were unsatisfied because new features were being added despite old features remaining broken. As this went on, new DLC lost popularity more and more.

Utopia came before the patch that broke many of the game's systems and remains the most recommended DLC. Megastructures and Hive Minds are very popular features (despite hive minds being largely abandoned after the release of the DLC and only recently getting some love).

The free patch that came with Megacorp is when the game broke, and so it and every DLC after it tend to get the backlash. Federations, despite not working very well on release, remained popular because it added more politics, which is what people seemed to want. Its features have improved since Paradox started patching the game's many problems, which rendered the AI too broken to properly engage with a lot of features, especially in Federations.

Overlord, the most recent DLC, would have been more popular had it not been such a buggy mess. It actually added some nice features like orbital rings, that really do add a lot. I suspect that over time, like with Federations, it'll be seen in a slightly more positive light.

This is the Paradox business model, though. It seems they contract out work for new features and give them the mod tools to add them. As a result, things don't work well. As the engine is improved and the mod API is refined, this will get better. Sadly, though, it remains another example of the game industry of selling a broken product now with the promise of fixing it later. The result is going to be mixed reviews (which would be negative reviews if Paradox weren't actually fixing things eventually).

/r/Stellaris Thread