This game was recommended to me while buying Sins of a Solar Empire Trinity (also a superb 4X game), something I knew was good and had been meaning to get around to for a while Sword of the Stars had good reviews so I figured why not and tried it.
I was blown away.
The technology tree is vast and incredibly dynamic and every game you will randomly have or not have certain non-core techs. This means that even in a game where everyone is human or another species, they will all be very different. One side might have advanced energy weapons, while another specialises in biotech. Each species has a leaning in what they are likely to be given - except humans, as ever the jack of all trades master of none.
Every species has its own method of FTL. Humans use a node drive which allows them to travel between gravity wells using gravitational fractures in space time called node lines. This is fast, but direction restricted and they cannot stop en route.
The Hivers on the other hand (bugs), have no FTL but have gate ships. They travel everywhere sublight (needs a little suspension of disbelief, since while VERY slow this is still impossibly fast for the sake of the game) and when they get there they set up gate ships for instantaneous travel later.
The Tarka (lizards) have traditional warp middling in speed, the Zuul bore their own node lines which they have to maintain, but can't use natural ones. There are six sides in total, all different - I'm quite fond of the Liir (wale/dolphin type species).
You can design your own ships. As you progress in research you unlock different modules and you can totally customize and name your own ship classes. Even within a module you can vary the weapon mounted on the hard point. I'm enjoy the spinal mount module for destroyers (the smallest ships size), it lets you give them a big cruiser sized gun. Obviously you can also customise maneuverability and scanning capability and all sorts.
Strategically it's turn based, but drops into real time for individual space battles. Within this you have great fleet control and can target specific enemy systems and weapon mounts.
Additionally, it has amazing maps with fantastic random encounters. The maps are 3d and you can have spiral galaxies, clusters, spheres, customize how many stars, almost anything you can think of. Von Neuman machines wander around and will randomly attack colonies, there are also lots of other great ones for which I won't spoiler the surprise.
On maps bigger than 50 stars, every turn after turn one hundred, there's a one percent chance he (or another 'grand menace') will show up. You get one per game.
There's also a great trade system, involving securing galactic grid sectors, assigning them freighters and having to keep them escorted to fend off raiders. You can even raid enemy trade routes.
Finally, this game manages to be awesome and hilarious. The human engineer voice who tells you how ship design and construction is going is basically Scotty from Star Trek. They manage to tastefully reference every sci-fi and still keep it good. Stargates, hyperdrive, photon torpedoes, it's all there.