To be put bluntly, it's very bad.
Or rather, it's good. For a mahwa at least.

Tower Of God seems to suffer the same fate that all currently made mahwas do: Interesting premise; Terrible writing. This paired with its atrocious at the beginning, laughable in the present, art really made reading around 486 chapters of it almost brain death inducing.

Can we go back to the art quickly? How is it humanely possible to improve this little in the span of 10 years? How? How do you go from something that looks like a bad rip off of Picasso's cubism in its absolute lack of fundamentals of art, to something that just looks like a 15yr old kid with a refill pad and ball point pen drew? Let's not even get started with the panel composition that rivals even Chris-chans fabled literary masterpieces. And yes, before you think anything, the art is very important when it's an action based, primarily tournament arc based story.

About the story: What is the deal with this structuring? Who thought it was a good idea to have a currently 10 year old mahwa focus 90% of the plot structure around tournament arcs? Off the top of my head? I could think of maybe three (3) interestingly setup tournament arcs, which may sound like a lot to non-readers, but keep in mind that if a tournament in TOG isn't happening, then you can bet the writer is trying his damn hardest to find another way to get the characters into one. The sad part is, is that it can't even fall back on amazing fight scenes because the art is so deviant art tier that none of the fights feel impactful.

The characters suffer so greatly because of this, outside of Bam, Rachel and Khun almost no one gets development for more than a few pages. You're introduced to so many characters that are inherently important, but instead of being fleshed out are almost just seen as ways to develop the plot, which is even more of a shame because some characters having genuinely interesting things about them that could make them really cool if they were just developed. But nothing can be developed on for too long because the mahwa is structured around its weakest point: the fighting. If the mahwa simply took the time to just sit down, no fights, and to just focus on characters, to solidify their existence and to make it more than just "I have to be here for x" or "I'll do this for y" then the mahwa could've actually been really good, despite the art.

That being said, characters also heavily suffered from mahwa character design philosophy.
Oh you don't know what that is? I'm not surprised because it doesn't exist. I don't know why every single mahwa Ive read seems to do this except for maybe one or two, but what is up with these abysmal character designs? Everything is so boring and there's very few unique silhouettes that it makes characters first impressions awful. Look at Bam, he literally looks like a stock background anime kid. This looks like designs someone found by typing "Anime Boy, Anime Boy with white hair, Anime Girl with Blonde Hair" into a generator and this is what came out. To be fair, as the series goes on future characters have a higher chance of actually having a briefly thought out design. Haoqins design is alright, Love Mule's is at least unique and Urek's is pretty cool, but I digress.

So what are you left with when you develop the story based around mostly fights without focusing on the majority of your characters?
1) A whole cast of undeveloped characters outside of 3 VIPs
2) An interesting premise and world that feels like outside of specifically tailored filler scenes has been not developed enough
3) Interesting narrative ideas that don't go on to be fully realized due to poor writing
4) A magic system with inherently very little rules outside of "if you have more reserves, you're better than others"
5) Power level spikes and inconsistencies that make Dragon ball look like it's a balanced and consistent show
6) And an overall time waster that somehow has become insanely popular on premise alone.

But hey, if you like mahwas, it's probably one of the greats :)