As this is an early access game, this review applies to the state of the game at this time(2014-8-22)
An interesting game that is best played with friends, Interplanetary puts you in control of a planet pitched in a fierce battle against the other players (And the developpers hinted AI may be coming soon) by shooting at eachother with railguns, missiles, lasers, and superweapons. This sounds easy enough but you'll find that when you need to shoot your opponents, your railgun will be facing the other direction due to your planet's rotation. Your lasers don't hit anything but air and empty soil because your opponent has worked on counterinteligence, and your missiles were brought off course by the gravity well of a passing gas giant. He takes the shot, but misses you just barely. And the gravity well of your planet redirects those railgun shots right into the orbit of a third player.
I did not expect it, but it is surprisingly challenging in your tactical and strategic choices. Do you build everything nearby so the early game railguns will do barely any damage at all, with everything you have fitting nicely under one defence structure... or do you spread out everything so a superweapon can't hit everything at the same time and destroy half your buildings with one well placed shot? Who do you aim at first? That guy who keeps shooting railguns at you and is obviously out for blood, or the guy who is peacefully building his war machine with mines and data security centers? The list goes on, but it has more than enough variety to allow for plenty of experimenting while it avoids having a single strategy that will always come out as the best.
It is certainly worth giving a try, with plenty of decisions and choices to keep you thinking, but fast paced enough to get through a game without spending your whole day on it. (Average, casual games I played with friends lasted about 1-2 hours)
For 10 euro, I would say it's worth it and recommend giving it a go. If you're not convinced, keep an eye on this one for when it goes on sale