Let's get this out of the way, this is still a console, and it won't give you the same gaming experience that a high end gaming PC will. That being said, no gaming PC priced under 750$ is going to be able to run modern games at 4k, much less play 4k Blu-rays, and even PCs priced under 1000 are going to be limited in the 4k department, unless you're a builder who knows how to find parts cheap.
If you've got better things to do than fiddle around with PC settings, on a budget, or just don't game enough to justify a 1000$+ rig, but still want to make the most of your new 4k TV, this is the best choice for you.
There's not much to say here, it has a 4k Blu-ray player, and it will play them back in 4k/HDR10. You'll have to install the free Blu-ray app from the Xbox store, but I can't complain about it too much. Only real downside in this department is a lack of settings to fix audio lag, but most TVs and receivers that you'll be plugging this thing into will already have those settings anyways, so it's not a big deal.
This is the feature that sets the X above its less expensive sibling (the S), which also has a 4k Blu-ray player. The 4k resolution's impact on gameplay is subjective, as most games don't have a huge difference outside of more crisp edges and some antialiasing improvements, but the real game changer is the HDR, and good Gandhi does it change your experience. Keep in mind, I have a Samsung MU8000, so your model of TV may produce difference experiences from mine... But on my TV, the HDR is incredible. Colors are more vibrant, blacks are deeper, whites are brighter, but more importantly... The details stick around. In both bright and dark spots, rather than creating black and white "blobs". This feature has ruined me forever, and it's hard to go back to SDR now that I've seen how amazing it can be.
Keep in mind, not all games support 4k/HDR, but the library is pretty big, and it keeps growing, with most big games having 4k/HDR updates.
Don't have a 4k TV?
If you don't have a 4k TV, I would still recommend this for a few reasons. For one thing, even if you're running a 1080p TV, the extra power under the hood will be dedicated to running the game smoother, with most games hanging out around the 60fps mark. You're going to notice a big improvement in game performance, in fact I run many games in 1080p with HDR just to get those 60 frames. Also, in some cases, games will have better graphics than the standard Xbox one or Xbox one S. A good example of this is Ark survival evolved and the Xbox one X only "enhanced graphics" mode.
Another benefit you get even without 4k is some degree of future proofing yourself. 4k Blu-rays will play in 1080p if not hooked up to a newer 4k tv, so you can start stocking up on your media before you decide to invest in a 4k TV.
Another great thing about this console is its size, and how quiet it is. It's not only tiny, but thanks to it's vapor chamber cooling system, it's almost silent. The only time I ever hear three thing is if I leave it running in game, and everything in my apartment is dead silent, and even then it's just a light pulsing hum.
Contrary to what the PC master race knobjobs will tell you, this is a fantastic piece of hardware, and will give you a gaming experience that similarly priced PCs can only dream of.
If you don't care about the 4k HDR gaming, or boost in game performance, and you just want a 4k Blu-ray player, save yourself a few bucks and get yourself the S, which also has a 4k Blu-ray player.