S7 has two major problems. One is probably objective, the other is from my personal feeling.
Objective one: Low information density. Excluding the season opener and the final episode, almost every other episode has an "OK, I already told you the story. Move on to the next!" vibe in it. If we say that S6 has many small pointless arcs, then we can say S7's main arc has many small pointless moments.
Personal feeling: The potentials. Their interactions with the Scoobies are embarrassing to watch. They are like a bunch of apes mimicking human. They are a poor parody of the Class of '99 in "The Graduation Day, Part 2". When Buffy's classmates are playing army, it feels empowering, because it has a background of three seasons and "The Prom" to help making sense and laying out the tone. When Buffy and her younglings are playing army, I just want to claw a hole in the ground and hide.