If you're pondering over watching Nanatsu no taizai or not, there is one question you should ask yourselves: do I like shōnen anime? Because here's your typical one, surfing on familiar waves such as Fairy Tail and Dragon Ball, bringing its own share of epic. So, if the answer is yes, it's unlikely you won't enjoy the show.
Even without spoilers, you know what to expect of that kind of anime simply from the genre they belong to; that's the problem with stereotypes and this show is no exception. In fact, it doesn't even try to break the stall, doesn't try to run free and surprise you, or to amaze you in some way or another. Instead, it gives the feeling of honestly doing its job, and with enjoyment. What could be seen as a flaw leaves eventually a rather good impression. Yes, it's classic! Nevertheless, the story is very decent and the protagonists offer enough interest in every aspect of their characterization to make them more than likeable (now, I love giants). In the end, everything contributes to a very entertaining show, well-paced, which doesn't take his audience for fools and simply shares a common passion for the genre.
The art might look a bit weak or old-fashioned, but it's not a bother and, somehow, it contributes to the charming and colorful Dragon Ball side. That, and fist fights, super powers, transformations and the quest side. From Fairy Tail we got more of a general tone, with heroic fantasy, magic, mysterious pasts and motivations, friendship and dedication. So, once again, even without exploits in the direction and average animation, the job is pleasantly done.
Enough to say the best part is there will be sequels.
Enjoy!