There's irony in the fact that 4X games like Horizon are about forging forward into the future, but are always at least spiritually caught back in 1996, in the shadow of Master of Orion II. Horizon more than most is in that game's shadow. Its—being polite here—retro graphics, clunky UI, and general lack of polish set a poor first impression that never blossoms into something that lives up to either Master of Orion II, or other attempts, like the mighty GalCiv 2.
It's not a game without ideas though, especially early on. For the most part, it's the standard space conquest drill, about humans venturing out into a galaxy that's already been ticking along just fine without them, and a race to scoop up the best planets, invent new toys, and forge alliances capable of withstanding threats from both inside and outside, at least long enough to get the upper hand. It's a slightly more involved galaxy than usual. Its quests give the various alien races a chance to show some personality (though they can be switched off if you prefer), and there's a clever tech system where inventing or being given a new toy is just the start and research is needed to perfect it over multiple quality tiers. This is nowhere near as exciting as getting something new to play with, but it does offer interesting tactical options and the chance to focus your empire's skills.
The problem is that while all this works well, the bulk of Horizon soon becomes a chore. Simply getting started is a problem, thanks to a very basic tutorial that does a mediocre job at best of explaining the core systems and then just vanishes, leaving you to stumble through the rest on your own. It's a micromanagement-heavy game too, becoming more so with each colony founded or task force assembled. That isn't necessarily a crime, but here it's coupled with very little reward. The quest system sets a character bar that the regular diplomacy doesn't come close to, with the aliens suddenly becoming terse to the point of rejecting deals by declaring "Not!" like a bad '90s comedian.
By far the worst part is the combat, which comes from a universe where Sins of a Solar Empire clearly never existed. The turn-based scrapping is so dull and long-winded that even handing it to the computer to handle is somehow annoying, while actually playing it out is a shortcut to cranky old age.
This is a shame, as the basics of Horizon work and the new things it does bring to the table are well executed. What the genre's greats manage, however, is a spark that elevates the core systems into a genuinely satisfying sense of galactic conquest. Horizon does occasionally manage a quick flicker of one, but it's far too quickly snuffed out to ignite any passion.