Starships Unlimited 3 has all the usual tropes of the 4X genre--a galaxy to explore, a deep tech tree, diplomacy with alien races--but with a major difference. The emphasis is, as the name suggests, on your starships. They're highly customizable, and the construction system makes each one you (or your opponents) build considerably more expensive than the last, so that even the largest civilization rarely has more than a dozen in play. This actually works to the game's advantage, because the starships become your protagonists, each individually interesting, and the missions they embark on have something of the feel of Star Trek to them, rather than being another mundane task in the long and (often) tedious grind of a typical 4X game.
Andrew Ewanchyna has been working on Starships Unlimited for five years, gradually improving it over time; it's now a highly polished little game. Not without flaws, mind you; this is a complicated game (as most 4X games are) and while there's a fair bit of in-game help, the manual is organized as a reference rather than to teach you how to play, and a tutorial would help a lot. But if you're willing to invest the time to come up to speed, it is a heck of a lot of fun.