Thus far, the centerpiece of a Celtics offseason predicated on "fireworks" has been free agent Evan Turner. Boston's only trade of the summer brought back Tyler Zeller and Marcus Thornton, and will ultimately help the Cleveland Cavaliers acquire Kevin Love.
The Celtics haven't made much of a splash this offseason, but one of the most respected NBA writers thinks highly of what the team has done.
NBA.com's David Aldridge ranks Boston's offseason the 4th-best among 30 NBA teams, coming in behind Cleveland (duh), Chicago, and Charlotte. Aldridge praises Boston's draft picks (I agree with him here) of Marcus Smart and James Young, as well as the signing of Avery Bradley. He credits the team for adding "numerous assets" without trading Rajon Rondo.
I don't think the Celtics have had a bad offseason, but I wouldn't say it's been particularly good. A glaring omission in Aldridge's analysis is the Celtics' failure (so far) to turn all their draft picks into anything tangible. Maybe a big deal is coming, and you have to credit Danny and company for not rushing into any bad moves, but to me it's hard to rank them anywhere else but the middle of the pack.