For sure, reviews are important. In fact, reading feedbacks posted by traders is the easiest way to learn more about the broker and the way it works with traders.
Another important aspect you should pay attention to is regulation. To my mind, it is better to work with brokers licensed by reliable financial authorities like British FCA, German BaFIN or French AMF. These authorities implement strict requirements applicable to anyone offering trading services while it is quite easy for the broker to get an offshore license. So, first of all, you have to take the license number published by the broker and use it search the register maintained by the appropriate authority to check the validity of the license and the list of permitted activities. There you can also find information regarding any sanctions imposed against the particular broker.
Then, read carefully the Terms and Conditions (or the Terms of Service) published by the broker. This is the main document regulating your relations with the broker, so pay attention to the rights of the broker. For example, some of the brokers reserve rights to cancel trades or revise their results or other provisions that are quite unfavourable for the trader. If there are any limitations on withdrawals, they would be also set forth in the Terms.
Of course, such aspects as commissions or instruments available are important too, but they mean nothing if the broker commits unfair actions.