It's very easy to criticize a paper's execution while at the same time supporting it's line of inquiry. Just bookend the review with stuff like "This is a very

It's very easy to criticize a paper's execution while at the same time supporting it's line of inquiry. Just bookend the review with stuff like "This is a very important topic that deserves rigorous scrutiny" and "I fear the authors' failure to address the points listed above weakens their conclusions." This kinds of reviews are actually the most incisive, because it means the reviewer cared enough to really reason through your arguments and find the flaws in them.