In order to have good inbox deliverability; you need a dedicated IP. With MailChimp, you are piggy backing off of everyone's sender score. Therefore, if some other person is sending to a bad list, it will affect your overall deliverability as it is all coming from the same domain. Another major issue is the lack of features - the product is very basic indeed - and the fact that very little tech support is available.
Mail Chimp is a slight step up from Constant Contact. I would look fully into all of the benefits of paying for a full service ESP vs this platform. In the end, the extra cost is more than made up for by the superior feature set and resulting efficiency.
If you just want an email program to do batch and blast emails with no customizations and don't care what your send metrics are, then MailChimp will work. But this is not a good solution for any but the smallest and least sophisticated organizations.