I'm going to try to answer this without touching on the "dog whistle" issues, and just simply ignore them.

Star Trek Discovery (STD) actually has some good qualities, mostly it has insanely high production value. Easily the highest production value of any of the Star Trek series. Though that same production value to some degree is also part of its downfall.

First up is the Klingon redesign/retcons. Klingons are INSANELY well established in the ST universe. They have fully functional and actually spoken language, their culture, religion, and so on has been rather deeply explored and understood. STD as a whole basically abandons much of this, they keep the language but otherwise more or less butcher decades of story telling and lore to create a new Klingon race. The fact they kept the language is only made worse by having novels worth of dialogue spoken in Klingon and subtitle translated.
A fair amount of the changes to the Klingons broach into dog whistle territory, but basically just suffice it to say they took a well established race and completely remade them visually, culturally, religiously, and basically by any real measure you could have of a race outside of their language and then they use that language badly in terms of ease of watching.

ST, in all its franchises to a greater or lesser degree is hopeful. Its about a utopian future, humans have become better as a species, old issues have been resolved and mankind as a species is united in a utopian idea and the utopia WORKS! I don't always agree with the politics and ideals of the ST universe but I still enjoy it and I can accept unrealistic premises in fiction I can accept an idealistic utopia existing in sci-fi and its part of what makes ST what it is as a franchise. Its a fantasy about a better brighter future, it carries with it an undertone of hope.
STD almost entirely abandons this idea. The main character has basically incited a war and spends a fair amount of time in the pilot episodes as a prisoner because of her actions. The Federation is not shown as an idealistic utopia but instead in a much more realistic light. They truly care about borders, politics, and even take action that would would have Kirk, Picard, or Sisco flipping their shits.

Star Trek as a whole has a message and a story for every episode. Sometimes its just some character development without much commentary, other times it has some real social commentary. STD on the other hand is a bit darker and flashier, its a series and the episodes cannot stand on their own merit and each episode is simply part of a larger picture. DS9 is known for its "dominion war" arc, but realistically even throughout that arc its being told and experienced through traditional single serving ST episodes.

STD if it was named ANYTHING ELSE would be an unremarkable sci-fi series. It has high production values but so far the series as a whole doesn't really stack up to the great ST series. It also takes some pretty big deviations from what ST was and is both about particular aspects of the lore such as with the Klingons or just with things like how the narrative is told.

Basically instead of being a hopeful utopian sci-fi fantasy, with some social commentary added in rather tastefully. STD is basically a flash in the pan high production value sci-fi series that is more inspired by Game of Thrones than TNG or DS9 to help promote CBS's streaming service.

I would argue it has further issues with agenda pushing unlike anything an ST series has ever seen before. Though these issues largely become dog whistles and become grounds for dismissing the series or the person writing the information about the series so I've tried to stay away from them. I'll just simply note that such polarizing issues do exist.