Horizon is an imperfect product. It's better than many of the generic half-baked 4X games which are flooding the market as disposal-ware, but there are some very real drawbacks which limit the enjoyability of the game.
For newcomers to the 4X genre who are looking to sink their teeth into a strategy game with some structure and a relatively low learning curve and don't mind the dated graphics, I'm giving this game a thumbs-up.
For veterans of the genre, who are well-versed in games like Endless Space, GalCiv II and III, Distant Worlds or the Sword of the Stars franchise, I'm giving this a thumbs-down.
For starters there are some very unique strengths to this game which are stand-out from the rest.
Although almost every 4X game features the same exact tropes (types) of races, Horizon manages to give the in-game civilizations a sense of substance and personality which many other games lack. The in-game universe may not necessarily be as flushed as Endless Space, GalCiv or SotS, but the races present in the game are tweaked just enough from their stereotypes to make themselves unique---and the uniqueness of these races lend themselves to an almost genuine interactive quality. Species traits are certainly more than just window dressing, but the mechanics from one species to the next are mostly identical (unlike, say, GalCiv or ES, but much better than the generic games on the market).
The research and development process in the game is a refreshingly unique take on R&D systems. Unlike most games, where R&D focuses on one single tech at a time, Horizon has a system similar to the research points and tech levels structure found in Paradox's Hearts of Iron 3---with a measure of blind development to make things even more interesting. The way breakthroughs are often realized isn't through normal R&D channels, however, but by finding artifacts and other neat little details hidden throughout the stars. Exploration directly leads to new technological development, which makes the R&D system a lot more dynamic than most other 4X games out there.
Unfortunately, the R&D results don't feel particularly "real" in-game. For the vast majority of them, they are simply stat-modifiers. Advancements in construction technology will make colony-building construction faster, but it won't change the buildings which are available. Advancements in weapons and propulsion will add new weapons and subsystems which can be deployed, but ship-types are fixed from the start. Just as planetary development is strictly linear for each class of building, so too is ship design and deployment.
Ships are limited. Significantly. In contrast to some of the generic disposal-ware games on the market, 16 unique ship-models, limited to four variants in four size-classes may seem like a nice spectrum for deployment. When contrasted with the dynamic models presented in Endless Space, or the complete from-scratch construction system for GalCiv II and III, or the custom-function design approach used in Sword of the Stars, ship design feels incredibly flat. Ship design is very strictly limited to a handful of weapon placement positions and placeholders for whatever systems are available for use. All four hull sizes and variants are accessible to the player from the start, no additional R&D required.
It wouldn't be so bad, but the models for these ships look extremely dated once they engage in combat. The graphics look like they would be perfectly comfortable in the mid 2000s, but even against some of the generic disposal-ware 4X games, they look dated. Similarly, it's a very nice touch that Horizon has animated cut-scenes for first contact moments and other milestones, however, these cut-scenes too look like they are from the mid 2000s as well.
In summary, Horizon is a very mixed product. Some components feel incredibly well thought-out and they look great. Other components look rough, even dated, and seem to be poorly conceived and weak in implementation.
Ordinarily, I don't care about sales----usually, I'll argue that a game is either worth buying full price, or not worth buying at all---but this is not a product worth paying full-price for.
And the conclusion? If you want a straight-forward 4X game with some meat but not the level of complexity which the best-in-class games demand, then Horizon is a good solid choice, as long as you don't mind some of the graphics and other limitations. If you're a veteran of the genre, looking for the next breakout product, this probably isn't it. If Horizon has a sequal or a complete overhaul to ship design and deployment, and creates new cut-scenes from scratch, Horizon could start moving towards its' potential.
The potential is here, but it has yet to be realized.