If I had to describe Absolute Duo in just a few words it would be excessive fanservice, repetitive action scenes, and pointless plot. Allow me to break things down a bit further.
This show has a super basic premise, protagonist goes to a new special school to train his powers, and of course, he has a power that is a little bit different than the others students. This is about as basic as it gets as far as stories go, so I really need to be impressed with some new original details, or some really great characters to like a basic story like this. Absolute Duo offers absolutely nothing that got me invested. The story does evolve slightly from just day-to-day life at school to fighting some generic villains, this part is honestly even worse, and for the last three-ish episodes I was just extremely bored by all of the fighting of villains. As far as story goes, Absolute Duo offers absolutely nothing that hasn't been done 10 times better but a bunch of other shows.
The animation is fine, pretty typical, a little plain, but objectively well done. The action scenes are repetitive and boring, but the movement is animated well. The show is fine to look at.
Intro song was nothing special, not bad, but I skipped through it most episodes because I didn't personally love it. Background music during episodes tends to be fine, I noticed once in the final episode that there was some really overdone opera-esque singing that actually made me laugh by how overly dramatic it was. However, overall nothing remarkable in the sound department.
The characters are probably the worst part of Absolute Duo, every one of them is just defined by two personality traits at most and has no depth. I can forgive an anime for quite a lot if it manages to get me emotionally attached to the characters, I felt absolutely nothing for any of the characters in this. Tor is a typical harem anime protaganist and is pretty boring, Julie tends to not show her feelings outwardly and is a little clueless most of the time, Aoi has no personality other than wearing glasses, Imari is sporty and confident, Lilith is demanding and annoying, Miyabi is shy and turns evil for a little bit, Rito is the sexy bunny teacher, Tomoe is smart and driven, Ryuutarou is a buff guy that literally only communicates in grunts. K is one of the most cartoon-y boring villains I've seen. None of the characters have clear motivations or fleshed out backstories, no one is relatable, no one is likeable, it's just a bunch of overdone tropes with no substance.
Some Closing Thoughts:
One of the main gripes I have with Absolute Duo is the amount of time it wastes on fan service. I get it, it's a school harem anime, what did I expect? But it is truly ridiculous how much fan service there is, and all of it is overdone cliches. Stuff like bath/shower/hot spring scenes with naked girls, a whole beach episode where everyone's in bikinis, a girl losing her bikini top, a girl losing her panties, when any girl makes any movement her boobs move all over the place, panty shots, gym shorts that are basically panties, boobs being pressed against the protaganist's back, girls falling that results in some sort of boobs in someone's face/crotch in the face, girls groping each other's boobs, I mean the list goes on and on. I'm not entirely opposed to fan service, there was quite a bit of it in No Game No Life but I still really enjoyed it, and that's because it had interesting characters and story. Absolute Duo should have spent even half the time it spent on pervy camera shots and put it into making me emphathize with characters, or made a more solid plot.
I guess this is some people's cup of tea, so if a harem anime with a lot of fan service and not a lot of anything else sounds good to you, I would recommend Absolute Duo, but for anyone else, your time would be better spent watching anything else.