Well... unless it's something really new, not a small change.
Some changes are not amenable to small diffs.<p>In that case, you don't just "review the diff", diffs are <i>VERY</i> limited. Lots of context is lost (you still use it as a guide, but it's not enough).<p>So, what to do?<p>Do a code walkthrough, involve reviewers early, if you're on the reviewing end, check-out the thing and navigate the code with whatever tool will help you understand it best (IDEs, whatever).<p>Reviewing a large change should be closer to pair-programming than a classical code review.