We run multiple Wordpress Multisites and they are very customizable. Assigning custom domains to a Wordpress site is not supported out of the box, but with a domain mapping plugin, you can do it. We have a multisite deployment with 50 sites running on it and all of the sites have their own domain names. The backend url is even mapped so the client does not have to look at your domain. If you have any other questions, let me know. I have been working with Wordpress Multisite since it was Wordpress MU.