Stellaris is Paradox's newest GSG. They did push out a big free update a couple weeks ago that made it a lot more playable, when it launched it was pretty bare bones. I'd say it's probably one of their easiest (but also the most different) GSG that Paradox has put out.
I think one of the main draws for me is creating your own alien civilization. You get to design your alien race from the ground up, starting by choosing your species (humanoid, avian, reptilian, etc) as well as their traits and their planetary habitat, and then you get to choose the government form and your FTL method.
For example;
It's also kind of cool that any civilizations you create will show up in your other playthroughs. So I can be playing as my scientific, peace-loving Ymorz Mandate, and then I might happen across my evil military dictatorship Hivemind.
Oh, and it wouldn't be a true Paradox GSG if you couldn't do some borderline Hitler-esque shit, like enslaving or straight up "purging" alien species once you conquer their planets. So there's that.
That said, I only have 50 hours in it so far (nothing compared to my 997 hrs in EU4), but it's pretty fun so far. I'm excited for new DLC to come out because Paradox DLC usually adds things to the game, instead of just adding back in stuff that was cut before release. Paradox regularly does Dev Diaries for all their games where they talk about player feedback and what direction the game is heading in the future.
But I guess ya'll can keep complaining about Paradox having a million DLCs while buying character skins for Rocket League or Borderlands. I guess as +1 collectors, it doesn't matter whether the DLC adds anything or not, it just matters how cheap you can get the "complete GOTY edition".