I'm going back further than most will remember, but 1970 has to rate as the worst.
Only one player, Dennis Wirgowski, ever started for the Pats - for all of three seasons, on bad teams.
1985 and 1997 were runnerups.
Some consider 2007 to be bad, but I don't when you look at the big picture - in other words, what the Patriots did with that draft capital (trading picks for Welker and Moss).
More recently, 2017, 2019 and 2022 are in the discussion.
As the years went by, Belichick did not adequately replace front office staff that departed, and it showed in his last few drafts.