Actually, I think they're too short. Missions should be deeply involved puzzles (being serious) with something going for them other that shooting someone or running to the next console that we automatically hack.
Now, what I would agree with is that there should perhaps be more break points where you don't feel so rushed, because I have felt that way before when I, too, had some "business" to take care of.
Some missions are 'zip zing done!' and some drag on for what seems forever. I like the change up though, it's nice to get a quicky now and then (innuendo intentional).
What I would like to see is the content in generate missions worked on a little bit, but given the limits of their system it is doubtful to ever really reach a level where it would compare with scripted episodic content.