One of the most damaging decisions ever taken by Makemusic was the removal of note-attached expressions in Fin09. I miss them almost daily. It was also patently unnecessary, since note assignment could have been blended with meas/beat into the barbell U.I. we have today. Their removal was the reason I eschewed every update between Fin08 and Fin12.
But that is water under the bridge. There are, however, still features from note-attached expressions that are missing.
1. Gracenote attachment. Gracenote attachment is a kludge, requiring use of the assignment dialog and guesswork as to what number to enter there (especially if there are a lot of gracenotes). Also, expressions don't scale to the size of the gracenote based on the setting in the assignment dialog. Nor do expressions attached to the gracenote position relative to the gracenote.
2. Moving notes around in Speedy leaves the expressions stranded. This is perhaps my biggest beef with the confiscation of note-attached expressions.
3. Layer assignment is also a kludge. It requires opening the assignment dialog, and it gets messed up if you are splitting two parts on a staff into individual parts. I'm not even talking about voiced parts, which still have the fatal no special tools restriction. I'm just talking about using TGTools->Smart Explosion to split them onto different staves.
There are probably others I'm not thinking of now. But those are the big issues that come to mind.