It looks like there are not any critical reviews yet, so I'll attempt to write one (Spoilers ahead). I am going to write a review that is purely based on the contents of this anime and assume that it is not adapted from a manga.
When it comes to shounen shows such as Nanatsu no Taizai, you can't be expected to watch it and learn something profound about life. They are meant to be taken at face value and usually, I just watch them for their tacky and wacky plot. Sure, the series is mediocre it has always been enjoyable until this entry that is.
Studio Deen completely butchered the art and quality standard that A-1 pictures set. It was nowhere near on par. You get really weird facial animations as well as still shots. Most of the action scenes seemed weak (literally, characters just seemed like they were punching cardboards) and most of the time, they were obscured by a huge amount of smoke. Perhaps an attempt by the studio to save money and time.
That being said, an anime can be regarded as passable if the plot redeemable right? Sadly not in this case. Characters were out of place most of the time and the dialogue (that is not exposition) felt incredibly redundant. Seriously, you might as well be watching an animated encyclopedia version of the anime; there would be no disparity. I like how they included more screen time for the side characters and not focus too much on the titular characters themselves. However, Ban is gone for almost the entire last half of the anime.
The execution of the story is so bland that it's forgettable most of the time. As with all Nanatsu no Taizai entries, ex-machina moments and plot holes are incredibly prevalent. The issue with this entry is there are no engaging or fun moments to cover up for these issues. Every single character evolves into some OP god when the plot needs them to, this time without explanation. Remember how the humans struggled to beat an Albion? Yeah well apparently now since it's the "last showdown", every holy knight can just blast through every single one of them. Maybe it's just because I have not been paying enough attention but honestly, I wouldn't even call it my fault for falling asleep halfway through a smoke-clogged fight.
TL;DR: With the number of fight scenes in this anime being clogged up in smoke, you'd wish you were in this anime because your lungs would die from the smoke before you'd die from Corona.