Maybe it's just me misremembering things, but I swear there was a lot less manga content covered in the first season than there currently is still to cover.
The conspiracy about the titans inside the wall
The torture and death of that priest
The appearance of titans inside the wall
The tower battle
The beast titan
Connie's mother
Sacha fighting off a titan with a bow and arrow
The reveal of Ymir being a titan shifter
The double-whammy of Armored and Colossal titans
Eren earning his first titan kill as a human
Eren getting kidnapped (again)
Hannes' death
Eren revealing that he's a controller
Erwin losing an arm
A bit about Christie's past
...and that's all there was translated as of several months ago, which was the last time I read the manga. There's a
lot to cover, even before they start adding bits and pieces of filler.