I believe Bishop Lennon served as the Apostolic Administrator of the Archdiocese of Boston after the departure of Cardinal Law.
Yes he was Apostolic Administrator after Law left, after being his Vicar General when Murphy was sent to Rockville Center.
Prior to that he was Rector of St. John's Seminary.
Prior to that he was Assistant for Canonical Affairs...there has been some evidence of him being linked to the Geoghan debacle but nothing 100% conclusive given his short time in the role.
Theologically he's probably a walk the tightrope type, it took until the current Rector to clear out the questionable faculty at the Seminary and while he was Rector they were still tossing guys for being "too rigid" (code for orthodoxy).