I switched to EventON from a different calendar ecosystem, and I have been amazed at how much is built into this calendar that I used to need separate plugins for. I'm now using the main calendar and three of the add-ons, and this combo has replaced ELEVEN plugins from our previous system. Everything /just works/ together, the admin interface is a pleasure to use, and the support is superb.
The only reason I took off a star is that, although some parts are infinitely customizable, other things are nearly impossible to tweak. There are no templates to customize the calendar views, and the CSS is impenetrable. I've been able to make some changes by getting answers from the support forum for one thing at a time, but it slows me down and it's frustrating.
Anyway, I'm mostly very happy with it, and I'm glad I made the switch.