In short, maxi menu CK is AWESOME! I have spent an incredible amount of time looking for an extension that will give me the capabilities of MEGA MENU, until someone recommended MAXI MENU CK. This module brings almost all features of mega menu (if not more) and it's completely FREE! There is no need to install complex frameworks and components, it simply works by itself.
The default template is not very attractive, however the menu is fairly easy to style and adapt to your needs. You have the ability to make several independent templates and then easily change them through the menu admin panel. The css files (actually php files) are well commented and designated so you'll have no problems working with them. I'm quite pleased with the results I have achieved with maxi menu CK and I don't consider myself to be proficient in css styling.
I have tested the menu with IE 7, 8, 9, Firefox, Opera, Chrome and maxi menu CK looks consistent across all browsers. I was amazed by this fact, considering that the menu features complex functions. The multicolumn feature is excellent and you can easily add support for more than 4 columns in the template files (should you ever need to do so). You can style individual menu items, modules loaded in the menu, basically everything.
But the best thing about maxi menu CK is that should you encounter some problem with the module, Cedrik is always there to respond and guide you to solution. He has responded promptly to each of my mails, and I know I have had some questions and problems.
Furthermore, the development of the menu is rapid, just look how many features have been added since the beginning of the year. I'm expecting this menu to only get better and quickly.
Just don't forget to use maxi breadcrumbs CK with the menu... you will need this module to hide the descriptions and functions you'll use to style the menu. maxi breadcrumbs CK is free, simple and issue free, so it shouldn't be a problem to replace the default joomla breadcrumb bar.
Thanks Vlado for your great review. I always make my best to help persons in implementing my extensions. It's a pleasure to see such great comment.