This is the Kengan Ashura anime review covering seasons 1-2. I won't be adding manga details such as differences as I have never read the manga. The anime is currently available on Netflix. There won't much spoilers.
Here's the summary from IMDB:
Kazuo Yamashita is an ordinary fifty-six year old man who one day is summoned by the chairman of his company and hired as a manager of a gladiator. He learns that these hired gladiators engage in battles called "Kengan Matches" to protect the corporate rights of the businesses they represent.
The anime I enjoyed it because I grew up watching martial arts movies with my father and family members. This adaptation has passionate narration on the various martial arts and fighting styles plus fictional martial arts while they mix in some scientific facts and trivia on top of it. Bit similar to Baki. There is some sort of Street Fighter inspired and supernatural elements with some fighters using "Advance" and "Removal" which they undergo a transformation to power up their combat stats.
The story begins with a set up of two main characters, Yamashita and Ohma, along with brief world building on the underground tournament of corporations and their fighters. Episode 8 starts off this enormous tournament and the end of season 2 doesn't conclude the tournament. The anime series' season 2 concludes on Ohma's match with Raian. As for character development, this tournament anime follows mostly on a formula of having a character backstory for most combatants during their debuts in these matches. Sometimes, this does outshadow Ohma and Yamashita in terms of screen time and character development.
Animation - some folks will be turn off by CG. I'm not personally turn off as I mostly consume anime. The CG is good as all of animation is done in CG which helps it look more consistent compare to other franchises that mixed in CG with traditional art style. My eye isn't as sharp. I feel the animation in Kengan is done well during battles with actions going fast. It doesn't feel stiff. The background and colors are not that great. Character models are detailed with how they illustrate the curve and muscle shapes of various fighters.
Music - it's unmemorable for me. With Netflix auto skipping endings and I'm skipping the opening manually, the soundtrack and music doesn't impact me much.
Violence, Fan Service, and Maturity Content
It's a mix of serious and light hearted comedy. There are a few deaths. The anime isn't dark and gritty. There are lot of adult jokes, innuendos (sometimes I miss them as I'm not culturally perceptive), and fan service (there are female characters who love muscle and yaoi and male characters who admire both female and male anatomies).
For violence, there are blood shed, stabbing (via fingers), eye gouging, shots below the belt, and neck twisting. I don't recall dismemberment. There are definitely no disembowelment or decapitation.
For fan service and ecchi content, there are no nudity or panty shots or grope/skin ship. There are sex scenes but you just see them hugging but not moving/penetration. They actually illustrate sperm impregnating an egg in the first episode. There are shots of male crotch with an erection. There are at least 2 or more characters who speak vulgarly about having sex, bearing child, or ejaculation. There are no rape scenes. There are not hot spring or bath scenes.
The character models and art style is good. The female characters look cute while the male characters whom are described as "Ikemen" are handsome in my personal opinion.
Overall, I recommend this anime to an older audience and maybe immediate fans who had a fill of anime. If you are a fan of martial arts, it's a definite recommendation. Just be aware, seasons 1-2 do not complete the tournament. You might want to read the manga or hope for another season.