It's a 4X game. You don't need me to tell you whether you like 4X games or not; either you've played one before, or you haven't. Instead, let's consider what differentiates Humankind from similar games in the genre - the most obvious (and common) comparison being to the Civilization series by Firaxis.

Speaking generally, each new entry (and DLC, although for simplicity we'll ignore that) in the Civilization series has added (or modified, or removed) pivotal new mechanics which fundamentally change the way the game is played. Civ 5 added the hex grid and removed unit stacking; Civ 6 added districts and a second tech tree for culture. At its core, Humankind is close enough to the standard formula that we can consider Humankind to be a spiritual Civ 7 (pending an actual Civ 7 release); consequently, we can examine the major changes that have been made and how this influences the experience.

Humankind has made a lot of stylistic decisions - some received better than others (for example the pollution mechanic, while incorporating climate change as a concept into the game in an interesting way, also lead to so much complaining due to abruptly ending games that it is often switched off as a game-ending condition). On a fundamental level, however, there are three major changes which define and differentiate it from previous Civilization games (listed here from least to most consequential):

1. The combat system. Combat has been completely revamped, leading not to a regression to the 'infinite stack of units' of Civ 4, nor the continuation of the 'one unit per tile' of Civ 5 and 6, but instead to a compromise between the two, where units of different types can be combined on one tile when out of battle (with the size of the stack depending on technological and cultural research, era and religion perks, etc). These unit stacks, when going into battle with an enemy, form a miniature, locked-off battlefield in which each unit occupies its own tile; reinforcements can be sent in (after an early game technology is researched), but units can't be sent out. This approach makes combat feel a lot more dynamic than in previous installments of Civ, often requiring more attention in placement, battlefield control, etc. The most striking downside is that the procedural generation of these battlefields by the game can be somewhat arbitrary, leading to a common situation where an otherwise easily-bypassable bottleneck becomes the only way to attack an enemy. Besides this, the ability to instantly resolve the battle is also great in speeding up the game, but can give completely unexpected results, and is often paid for with less efficient use of units compared to manual play.

2. Cultures/era advancement. The developers have recognised the real-life evolution and morphing of civilisations over time, and have incorporated this into an era advancement system which allows for far more complexity in each game due to the sheer number of culture combinations available. This, in turn, causes a really interesting interplay (especially in multiplayer games) as the cultural choices of other players influence your own advancement path, and vice versa; it allows people to lean into one form of gameplay or another, and even allows for some mitigation of RNG - if you've been dealt an environment unsuitable for one culture, another one might be more advantageous to take. Having been burned too many times in previous Civ 5 games after locking in a civilisation and starting a game without a given strategic resource, or inhospitable terrain, this approach removes this downside while - if you care about that kind of thing - more accurately portraying real-life civilisational evolution. In short, a great new addition.

3. The win conditions - or perhaps 'win condition', singular, because there is only one. This is by far the most important difference between Humankind and the Civilization series; the classic string of different victory conditions (send the rocket to mars, persuade the world congress, eliminate all other players...) has been relegated to simply ending the game, leaving the only way to win is to have the most fame points when the game does end - fame points, in turn, mostly being awarded through era stars earned through the different ages, relating to districts, influence and gold generation, population, expansion, and military aggression. This means that (particularly at higher difficulties) it's no longer sufficient to lean heavily into, for example, conquest and expansionism, in an attempt to wipe out your opponents and be the last civilisation standing; if your opponents are able to earn more fame points than you before you wipe them out (and they almost certainly will at higher difficulties), those eliminated civilisations can still win overall. This does add another layer to the advancement mechanic (are you going to delay advancing era and get more fame points, but potentially miss the opportunity to pick a particular culture?), but also forces a more well-rounded style of play, where neither total military domination nor scientific focus are enough to achieve victory. I wouldn't call this inherently better or worse than having multiple victory conditions - there is still some amount of leeway and creativity in developing your civilisation, especially at lower difficulties, so it's not like every game plays the same, or that the game is 'solved' - but it does represent quite a radical change in gameplay that might be unpalatable to some.

There are other, more minor things to quibble over - the landscape can be a little hard to read (the visual difference between a surmountable hill and a blocking cliff can be minimal at times), city stability has a tendency to fluctuate in ways that can be confusing and opaque, the population allocation is virtually non-existent compared to, for example, the micromanagement of Civ 5, and there can be some buggy moments - but all of these are ignorable and don't really impact the overall experience too heavily, and could even be revisited in later updates.

On the whole, while it doesn't quite reach the pinnacle of gameplay that lead me to sink a frankly embarrassing number of hours into 'Civ 5 with all of the expansions plus a balance mod', Humankind is a very strong addition to the 'real life'-style 4X genre, and a serious competitor to the Civilization series. Strongly recommend giving it a go to people both familiar and unfamiliar with this style of game.