The only club that was unable to put themselves back to qualify for the European competition is Napoli. They were the defending champions of Scudetto but they performed very poorly, and could not secure a place in any of the European competition due to change of their coach after last season victory. Maybe Napoli needs to replace their coach with a new one for a better achievement next season.
There was some huge variance for most of the clubs. Inter Milan was brutally solid, no need to talk about that any further. But at the same time I thought Juventus Turin might have a solid comeback from the disaster last season and for a long time it looked very good for them, but then suddenly they performed like trash.
AC Milan was similarly unstable. They had some great phases with many wins in a row or many games without a loss, but I think as soon as they realized that the Serie A championship could not be won anymore, players are calming down and are probably less excited about the games to come.
Bologna is the surprise of the season to me. They haven't only qualified for the Champions League, but they have also beaten Inter Milan in the Coppa.
And I am sure everyone agrees that the disappointment of the season was Napoli. I don't even know whether this was more like an exception or whether it was that one great season and they will now get lost in the middle of the table as a mediocre team.