It's very, very good. I haven't enjoyed a 4X game this much since SMAC... and yes, that is high praise.
It lacks a bit of depth that SMAC had, such as the Government/Ethics types but it's really hard to put down. The races are all nice and varied and as mentioned, you can always create a custom race if you're not happy with what you're given.
Space battles look decent if you decide to watch them. This gives you the opportunity to lay down special actions for Long, Medium and Close range engagement ranging from increasing your defences to repairing your ship or scrambling the enemy's targeting systems.
The whole idea of research which allows you to colonise different planet types, spreading to multiple planets in a system, terraforming them, exploiting them, managing their populations and either making the most of natural resources or dealing with negative effects produced by a planet is fantastic and some of the biggest fun parts for me. Heck, you can even survey planetary moons or put colonies on asteroids!
Been playing for a few weeks and it's been great. The release day patch made it even better. Definitely recommended by me.