I have actually been at UO twice on Jan 1, in 2001 and 2005, chaperoning HS marching band trips. It was quite chilly both times (downright COLD the first one), and we got there early. Before noon, the crowds were minimal, with short wait times on everything. After that it did get much more crowded, but if you get there early and ride the popular attractions first, you would probably be fine. My son and I debated getting the Express Plus, but I'm glad we didn't spend the money. We also rode from the singles line on a couple of attractions (MIB and Mummy).