We have been bless the last few years with a few very good 4X games, after a relative dry spell.
I am glad Horizon is one of the best, if not the best 4X game of the last few years.
The game is playable both as a traditional 4X game where you try to conquer the galaxy/etc and as a mix of that and light story intertwined with your conquering without taking away any freedom. The choice is yours.
You get to pick your race, a nice variety of them exists, including of course the humans.
Research, you have several fields/genres of research you can spread your research to, each of which has several "topics". You can choose to have either the field and/or the topic to have special focus/draw on your research points, Or not, leaving everything balanced out. Not all researchable itens are visible, for that you need a combination of luck, diplomacy and even finding a topic by accident during.....events. It's a very nice way of still getting surprise topics for research, even well into the game. It works really well.
There are sizes of ships you can use. From fighters up all the way to starbases. You can't design the outer looks of your ships, but you can do whatever you want for what they carry. Based on your research and limitations such as the size etc. For each size of ship you can save few schematics so that when you choose to produce them, you just pick what you want. Do you want a missile cruiser, check! Do you want a jack of all trades, check! Etc. Perhaps you want to add boarding troops to try and capture enemy ships, check! etc
The main galactic map is split in sectores (squares) similar to BOTF. Depending on the technology, engines, supplies, forward bases etc, you can move a number of sectors per turn. There is no limitation such as moving only through sectors which have systems in them. The map is zoomable with the mouse scroll wheel and focuses where your cursor is. When you click on a sector with a system , if there are any planets, a list of the planets in that system appear on the right side of the screen. There you can have a quick look of what the planets are (terran, barren, gas giant etc) and their size. Also if they have starbases or shipyards, at least if they are your own planets. Cause if they are the enemies' the intelligence might be innacurate... :)
You can survey planets and find "goody huts" in them, or nasty surprises orbiting them. You can terraform planets and of course colonize them. When you have a planet for yourself you can give orders to contruct builing types of specialization. Production, trade, research etc. You can build (or buy) as many as you want, limited by the size and type of planet and how many "slots" they have available. When you reach that limit you can't build anything more unless you demolish something else. That thankfully does not include military buildings. Military buildings which can be any of Starbase, Shipyard (allows constructing mothership type of ships, and better resupply and repairs of ships), missile defenses for the planet and barracks.
You can construct any number of ships you want, as long as you don't exceed the command points cap you currently have. Cap which can be increased for example by building starbases. When you exceed them you are going to pay a very large "fine" for each CP over the limit. If your economy can afford it, no problem, if not....
Battles. There are two types of battles, invasion of planets and space battles. Invasions take place in a static screen with a list of each side's army and equipment and a numbers only show of what is going on in the battle, ie, reduction of each side's army and equipment. At the end of the battle of course there is a result and one side wins.
That is of course if you want to invade a planet and not eradicate the population.
Space battles are in turn based format. There is initiative for each ship, based largely on the type of engine they have. Then you proceed and move, fire at an enemy with all or just a selection of your weapons, use boarding troops, launch fighters, etc for each ship. When you are done for a ship, if there is something more that can be done with it, but you don't want to do it, clcik Done and you given the control of the next ship if any. If there isn't any other friendly ship to "move" then it is the end of your turn and the enemy side/sides start playing. Yes sides, you might have battles with mor than two sides. Even if they are not allied to each other.
The battle are done really well and very fluid without any cumbersome gui, as the rest of the game is also very well designed for smooth playing.
Diplomacy, there are a ton of options you can choose, or the AI to choose. A variety of agreements from the simple non aggression pacts, to trade, research, supply, military agreements. And more.
Oh, and yes more than one race can have planet(s) on the same system. It can be very interesting. :)
All in all, a great strategy game, a great 4X game and a must play fo the fans of the genre. Just make sure to spend some hours first to get an idea of the scope of the game.
I have started a Let's Play of it, you are more than welcome to have a look. https://www.youtube.com/playlist?list=PLtpqh8ebqvxd6FUfWDn5Kj2DHC65ngY2U