Just bought the package on Steam (discounted at the moment) and I'm enjoying it a lot.
Stellaris shares a lot with GalCiv, MOO, SoaSE etc. but has its own take which is just a little different. Multiplayer is good, and real-time play a nice change from the usual turn-based approach. I like the interface a lot - it took moments to get to grips with it, but there is a lot of hidden complexity. Decisions have far-reaching ramifications, and the dynamics seem well designed. The overall look and atmosphere is good too - it seems a tad less cartoonish than most of these space 4x games. I played GalCiv for a while after getting used to Stellaris, and while GalCiv is very well designed, I actually prefer Stellaris now. I also appreciate that ship design/upgrade can be totally automated and ignored if you like.
The only thing I thought was clumsy is the switch from micro-management to automated sectors. It's a clever way to handle snowballing micromanagement, but feels too black-and-white. It would be better if there was the facility to choose from a wide range of settings that could be left manual or switched to automatic depending on the individual player's preference. As it is it feels like the one feature that was not quite fully developed by the time release day rolled around.
Also, if you have the game but have not yet tried the Star Trek New Horizons mod from the workshop the DO download it. Very, very well done mod.
PS - An Elite Dangerous mod for this game would be awesome