A stellar-looking title.
As a publisher Paradox Interactive has distinguished itself with titles like the Penumbra series (the predecessors of Frictional Games Amnesia: The Dark Descent and SOMA), The Magicka series, and the recent sim-hit, Cities: Skylines. As a developer they're known for their grand strategy titles like Crusader Kings. Stellaris is a bit of a shift, a 4X space game that borrows elements from their grand strategy titles.
On starting the game, you can pick the size of the galaxy and the number of different alien civilizations you may encounter. After that you can pick attributes for your race, with a certain limited number of perks, to which you can increase your ability or talent pool for the perks by taking flaws. In the demo I saw, they picked a "Xenophobe" flaw to free up more abilities, which had some clear effects further down the line.
The devs from Paradox know they have a rep for their games having intimidating systems, which led to them creating a more straightforward and clear set of gameplay mechanics for Stellaris. In addition, a demo system was created while building the game, with the in-game advisor to teach the game's systems to the player. If Stellaris is simplified, I wonder at the complexity of other Paradox titles, since there's so many systems at play in helping build and grow the space-faring society.
Gameplay starts at home, once the game starts, with allocations exploiting the planet's resources and doing certain types of research. Three research options are available throughout, and these cycle in a CCG-like manner that is appropriate to the level and abilities of your civilization, but slightly randomized based on what is available. No two games are the same as your technological level increases.
Exploration is handled with two resources, your military fleet, and your science ship. The fleet can investigate new areas and fight enemy ships, but the science ship is necessary for any in-depth analysis. The science ship captain can be exchanged for one your three planetary research department heads, which will give them new experience and different skills. The skills they bring to working on the ship can determine whether or not they make certain discoveries as well.
Upon encountering the first alien race, we saw the effects of the choice of creating a xenophobic race firsthand. While normally other options would be available to investigate or potentially negotiate, the only possible choice onscreen when confronted with alien ships was a single phrase, "Alien Scum". For a conquering race, choosing "xenophobe" is clearly a boon, providing an ideological basis for aggression, but for anyone prizing negotiation or peaceful advancement, it's probably less than ideal.
While they didn't have a save game to show us the endgame, the devs from Paradox were able to talk about the standard, boring post-game period, where alliances shore up and empires are defeated. At this point, you're kind of waiting for the game to affirm your win conditions, as you fully take over the universe—waiting for turns to play out and your reach to complete the final wave of expansion. Stellaris has a few tricks up its sleeve in the late game to keep things engaging.
With your races going to other planets, if you research the right technology, your planetary pilgrims may genetically modify themselves. This, plus the changing political attitudes of settlers can result in dissident factions that can try to rise up against the player in the late game. If you do too much research into AI for robotic helpers, they can become sentient and rebel as well. Another scenario involved researching too heavily into wormhole tech (one of several available faster-than-light travel methods from the start of the game), making more endgame issues to deal with than the standard shoring up of resources.
Stellaris is shaping up solidly as a 4X space/grand strategy hybrid PC game from Paradox, taking what the developer is known for and innovating and building off of that foundation. It doesn't have a release date apart from "coming soon" on Steam.