I started using Event Calendar back in 2006, when I was developing rosaleeshow.com. We needed a way to post upcoming shows (and list past shows) on our site — tried a couple plugins but this what did what I needed best and I found the code clean and was able to apply what little skill that I had to modify it to suit my needs.
More importantly, though, I think the mailing list and support I got is what made it worthwhile — I remember one instance, back in 2006, when I had a heck of a problem with a database migration and kept getting all sorts of errors … I think it had to do with PHP versions (or something) but I was really new at it and after going back and forth about it on the mailing list (see archive), Darrel took time to work me through the problem one-on-one in real-time troubleshooting it over instant messenger (see conclusion).
I couldn’t have done it without the help I got here. So, I would just say that yes, the plugin is great but it’s the people that make it rock and roll.