I really enjoy the artwork and many of the main characters, both the Seven Deadly Sins and Holy Knights, and think they have very interesting character concepts that I've not seen executed quite the same way in any manga before. I was roped in with the various love triangles, drama, and conflict between characters.
Unfortunately, I found myself mainly enjoying the backstories explaining their Sins and who they were, but not the chapters focusing on the present day and ancient past (which are a larger portion of the series) because many of those story arcs feel as if the writer is making it up as he goes along. He introduces enemies or a plot point, and then eventually reverses everything about it. It was interesting the first few times the author did this, because it was unexpected or an interesting twist, but now it's simply too repetitive or slightly less inspired. It's got to the point that I almost expect characters to reveal some big secret every chapter and there's too many characters in the limelight now for each one to have a deep and interesting backstory (not that it wasn't difficult enough already with seven main characters, eight counting the princess).
I would probably still recommend Seven Deadly Sins, but with this caveat: expect lots of Shounen-style fights, a decent chunk of fan service, and a very layered, sometimes confusing storyline that may require multiple reads to fully appreciate or enjoy.
