There are very few sitcoms that either make me genuinely laugh or surprise me ... this show does both, constantly. I started watching it after I fell in love with Chris Pratt in Jurassic World & Guardians. I heard people commenting on his wonderful, cute performance in this show so I gave it a chance ... and I could not be any happier that I did.
If you do not like it in the beginning, stick with it ... it gets better! But watching the show in its entirety allows you to fully understand many of the running jokes that appear throughout the seasons. And yes, it is fairly juvenile ("fart attack") but everything else makes up for it, if fart jokes aren't your thing.
The characters are human, they screw up, they love each other, they hurt each other ... but they all do the best that they can and, in the end, they care for each other and it always shows.
Watch this show, give it a chance :)