Recommended for the hardcore 4X fan only.
This game had THE worst launch I've ever seen (and I was there for Anarchy Online's launch). When this came out, nothing worked. Even the game option menus were disabled! It was a total and absolute rip-off where completing a game was downright impossible. But the developers worked HARD on the game after launch and have gotten this game on its feet.
This is the most detailed 4X game I've ever played. The star map is actually 3D and when battles happen you don't just roll some dice, you actually play the battles out in an RTS-style interface. Ship customization is done by picking from different section types then selecting weapons and special equipment for those sections. There's a pretty vast selection of equipment to pick from, too.
The big controversial part of this game for me is the mission system. When you tell a fleet to go do something (scout, patrol, whatever) in most games the fleet will go, do whatever it's supposed to do, and stay there. In SotS2, the fleet will go out, do whatever it's supposed to do for a few turns, then return home. You can change where 'home' is for a fleet but you can't select unpopulated planets for that. On the one hand, this makes sense to me. There are only so many peanut butter sandwiches you can store on a ship so it makes sense that they need to come back and restock. On the other hand, it slows the pace of the game down and adds complexity. I still can't decide if the extra realism is worth it.
The most enjoyable feature of the old SotS game is, IMHO, the variety in races and that translates over to SotS 2 just fine. You can't make custom races but each race is VERY different than the others. The method of propulsion is different, technology strenghts and weaknesses are different, some races can mount more weapons than others, and so on. When you get right down to it, switching between the Liir and the Humans in this game will give you much more different gameplay than building a custom race in most games.
So I recommend the game but only to the serious 4X enthusiasts looking for a lot of depth. If you're new the genre then you should probably stick with Civilization or Endless Space. If you come out of those games wanting a lot more detail then this might be your game.
P.S. Star Fleet Battles fans - you'll find your swordfish drones and plasma shotguns waiting for you. Enjoy.