Malevich is a code review tool that more and more teams within has started to use for code reviews. And now my team is also starting to use it. The really good thing with Malevich is how easy it is to use. It is easy to submit changes for review, it is easy to add a comment (just point, click and start typing without having access to the code). I guess the only thing I have against Malevich is that it is a tool. Because I think the most effective way of performing code reviews is face to face. But if reality is that most code reviews are done solo by each reviewer just sending emails is not great since it means that review history is basically lost (since it only lives in the reviewee's mailbox). Another problem I've experienced with pre-check-in reviews is that you cannot see the changes between the first attempt and the last since you only diff the last change with existing code. With a good tool you can diff intermediate versions too.
Malevich was fairly easy to install too. Once I had a machine with all necessary pre-reqs it took me a little over one hour to get everything to work including restricting security to the team and customizing the appearance of the application. Add another half hour to play around with it to learn how it worked. So if you're looking for a code review tool, I would first ask myself if you really need a tool and if the answer is yes, take a look at Malevich.