I have just tried upgraded to moodle 3.3 and have problems.
• In the previous version I have theme Serenity. I've got it among the themes to choose from even in the new version. But I cannot choose it so that the page gets that look.
• Images on the homepage and the different course pages are missing.
• swf movies refuse to boot.
I took a copy of the existing database and imported it into a new database, uploaded the files to a new folder, and ran install.php against a copy of the moodledata folder. It worked great when I updated another moodle installation to 3.2.
Thankful for tips on how to get the theme and images to show up in version 3.3.