Bought it on pre-order. Enjoying it a lot
Only bugs/feature complaints I have so far are:
1) Have to remove a ship from a fleet in order to upgrade it.
2) Can't really get much info on a specific ship if it's in a fleet.
3) When one of my starbases gets blown up I can no longer rebuild it, but the AI doesn't suffer that restriction.
4) When designing ships, I sometimes put some pieces together, save, then decide to upgrade the design a few times before I finally start building it. Although the build menu in the Space Yard will show only one instance of this ship, when doing upgrades you see multiple instances of this same ship, with the same name.
I believe item 3 has already been addressed in the last patch, but I'm enjoying how I can abuse the sensors right now so I don't wanna upgrade yet. =P
Overall lots of fun, I think it'll hold my interest for a while. Maybe not as long as SE4 since one of the things I love about it is that I can have it running in the background while I've got my IDEs up and I don't really notice it taking up all that much resources.