Well, large parts of the NT API are very close from Win32 API for obvious reasons, and so are often in the realm of dozen of params and even more crazy Ex functions. Internally there are redundancies that do not make much sense (like multiple versions of mutex or spinlock depending on which parts of kernel space use them, IIRC), and some whole picture aspects of Windows makes no sense at all given the architectural cost it induces (Winsock split in half between userspace and obviously needed kernel support is just completely utterly crazy, beyond repair, it makes so little sense you want to go back in past and explain the designer of that mess how stupid this is). The initial approach of NT subsystems was absolutely insane (hard dep on a NT API core, so can't do emulation with classic NT subsystems - so either limited to OS having some technical similarities like OS/2, or very small communities when doing a new target like the Posix or SFU was) -- WSL makes complete sense, though, but it is maybe a little late to the party. Classic NT subsystems are of so little use that MS did not even use them for their own Metro and then UWP things, even though they would like very hard to distinguish that more from Win32 and make the world consider Win32 as legacy. I've read the original paper motivating to put Posix in an NT subsystem, and it contained no real strong point, only repeated incantations that this will be better in an NT subsystem and worse if done otherwise (well for fork this is obvious, but the paper was not even focused on that), with none of the limitations I've explained above ever considered.

Still considering the whole system, an instable user kernel interface has few advantages and tons of drawbacks. MS is extremely late to the chroot and then container party because of that (and let's remember that the core technology behind WSL emerged because they wanted to solve the chroot aside userspace system on their OS in the first place, NOT because they wanted to run Linux binaries) -- so yet another point why classic NT subsystems are useless.

Back to core kernel stuff, IRQL model is shit. Does not make any sense when you consider what really happens, and you can't really use arbitrary multiple levels. It seems cute and clean and all of that, but Linux approach of top and bottom halves and kernel and user threads might seem messy but is actually far more usable. Another point: now everybody uses multiprocessor computers, but back in the day the multiple HAL were also a false good idea. MS recognize it now and only want to handle ACPI computers, even on ARM. Other OSes do all kind of computers... Cutler pretended to not like the "everything is a file" approach, but NT does basically the same thing with "everything is a handle". And soon enough, you hit exactly the same conceptual limitations (except not in the same places) that not everything is actually the same, so that cute abstraction leaks soon enough (well, it does in any OS).

On a more result oriented approach, one of the things WSL makes clear is that file operations are very slow (just compare an exactly identical file heavy workload under WSL and then under a real Linux)

So of course there are (probably) some good parts, like in any mainstream kernel, but there are also some quite dark corners, and I am not an expert about all architectural design of NT but I'm not a fan of the parts I know, and I strongly prefer the Linux way to do equivalent things.