Review forms have check boxes, and there is a temptation is
rely on the check boxes with minimal comments. But your
written comments are really the important part of your
review, and you should write comments that help both the
program committee and the authors.

In particular, be sure to cover the following in your written
comments; some of this material will be in response to questions
on the review form, but regardless it should all be covered
somewhere in your review:

1. Outline the paper.

2. Highlight the contribution of the paper, both what
the authors perceive it to be and what you perceive
it to be, as well as how significant it is.

3. State your recommendation and why.

4. State ways to improve the paper, but don't ask too
much (see both the previous and next sections).

The first forces you to reread the paper, which helps in writing
your review. The second is the hard part: you need to figure out
what the authors think is their contribution. The 3rd is one
that the program committee will focus on. Of these four, the 2nd
and 3rd are the important ones.