Critiquing in a workshop context is a skill worth learning. Some tips for the novice:
With the written critique already done (and to be handed back to the author), the critic need not worry about getting his words in edgewise. Thus the critic need not try to score cheap points at the expense of his audience. Rather, the verbal critique should be educational and constructive, contributing ideas to a large mental stew pot that the author, in rebuttal, stirs and tastes.
For folks unused to workshop verbal critique, reading the written critique is a means to start, if only as a means of structuring your comments. But as the critic gains experience, the verbal critiques are often quite a different presentation: they use the written words as an outline and then describe them. A good verbal critique is thus conversational, the critic talking directly to the author, and watching the author to make sure the author understands the critique (if not necessarily agreeing with it).
As the verbal critique works around the circle, themes become reinforced and sometimes established. What the first critic may tentatively hypothesize can become, by the fifth critic, an accepted conclusion. Or a particular area may become a topic of debate, with different critics weighing in on various sides. (In such circumstances, remember that you are not trying to win the debate, you are trying to give the author a full briefing on your views. The author wins the debate.)
Later critiques tend to be variations on melodies already laid down. If a half-page insight you were keyed up to deliver is neatly made by someone ahead of you, don't grind through your prepared remarks. Instead quickly agree with the point, or expand on it, or give more time to focusing on other issues. Similarly, things you may not have identified in your personal written critique may strike you, on hearing them, as particularly noteworthy or frivolous, and you can extemporize about them. Either way, voice your reaction to what has gone before--again, the critics are trying to brief the author on the full range of opinions.
Of course, don't hesitate to disagree with a previous critic, but give that critic the same respect you accord the author--that is, credit the critic with intelligence and perception in observation, just a different diagnosis or prescription. Point and counterpoint is the essence of a good workshop.
A good verbal critique may, therefore, be loosely outlined something like this:
Don't feel bashful about suggesting changes, even to the point of offering up major surgery such as a new plot line, collapse or conflation of multiple characters, or some other radical rethinking. The author won't be offended (in CSFW, we do this all the time), and is always free to decline your suggestion or to accept it. Or, in the authorial rebuttal, the author or the group can pick up a particular alternative and tinker with it in a variety of ways. Some remarkable inventions that amaze and delighte everyone, most especially the author, have come out of these spontaneous combustions.
The author is not required to say anything, but usually the author is filled with reactions bursting to get out. This is where your scribbled notes can come in. Take a deep breath and organize what you want to say--the critics, having shot their bolt, will wait attentively. Go back through your notes and talk about your reactions. Now you can explain what you were trying to do, what the critics missed, or what should have been there but isn't. ("It will already have been there," is a common authorial response to a particular apt criticism.)
Here also you can explore whether a particular solution does work, doesn't work, or might work. Having made all your responses, you can open up the discussion to focus on solutions and let the rebuttal devolve into a free-flowing discussion.
As you absorb this torrent of ideas, bear in mind that a detailed critique is the highest form of respect one author can pay another, and the more effort put into the critique, the more respect the critic has for the author ... and for the work being critiqued.