Clannad After Story is one of the best animes I've ever seen. Its deeply emotional, and funny from time to time; a perfect slice-of-life, while integrating aspects of fantasy. It can get pretty complex from time to time, so you definitely need to pay attention, but its an amazing anime nonetheless, and the soundtrack makes my heart melt all the time.
Clannad After Story definitely isn't for everyone; it gets confusing, complex, and may be overly emotional/deep. It's not a casual watch, but I would recommend it if you're into these deep, heartfelt animes. This show made me cry multiple times, and it's definitely a huge step up from the prequel.