I'll need to review the game in more detail, but my first impression is that the defense was relying a lot less on the linebackers in coverage, which was refreshing. The pass rush was ferocious, without the need to blitz. Bush was active. Minkah had a really strong game, and Pierre was impressive as well. Allowing an explosive Bills' offense only one touchdown on eleven possessions is remarkable. This is a big-play Steelers defense capable of carrying the team to a win, and it did so today.
The offense needs work. Very little in the way of openings for Najee, that 18-yard run he had was all of his own making. Ben was rusty, but he did make some key plays in the second half to prolong drives and help get the game under control. Props to DJ on a fine touchdown reception. It is plain to see that he's worked hard to overcome his issues last year with drops, and I expect him to have a productive season.
Overall, an unexpected win on the road against a very good opponent, leaving a totally different taste in the mouth than after the Bills game last year. The Steelers are going to need to keep playing at a high level, because to me the AFC North looks like by far the best division in the NFL.