The Dolphins started off last season very strong defensively, but their pass rush fell off considerably in the second half of the season and the run defense slipped as well. The Dolphins were second in overall defensive DVOA as of Week 9, but wound up finishing the season at 17th. How did they do that? By ranking 31st in overall defensive DVOA from Weeks 10-17. They went from second to 31st against the pass and sixth to 28th against the run after Week 9.
This isn't just a splash signing. In fact, I think other teams are stupid for not wanting Suh as much as Miami does