I thought the manga was underwhelming after watching the anime first. Compared to the crisp quality of the art in the show, the drawings look like chicken scratch.
Regarding what your friend said about "overreacting." The level of seriousness in the show is certainly dramatic, but I think it's what makes it fun to watch. It's dark, it's theatrically engaging, the animation style itself is so bold and striking that I can't help but get drawn into it. Interestingly enough, the humor in the show is subtly played. I enjoy that immensely.
Wae so serious, SnK.