It is crowded. The misinformation I see about October these days is crazy (not necessarily on this thread - most people here seem to know this fact by now, but so many other places don't).
October is the new summer - it is hot, it is crowded, and MK closes several nights every week for the parties, so that makes it feel even more crowded than it is when people pile in to get every minute out of it. Many more schools have Fall Breaks these days and the majority fall on these weeks. Columbus Day Week, even more so. We have gone both during this week (2010, 2011, 2012) and the week before Columbus Day (2014, 2016) and there is no difference. Both weeks were packed. Columbus Day itself is a day we avoid MK - we did it twice and when Buzz Lightyear's line crept up to 90 minutes, we got the heck out of there. That's a barometer for us that there are just too many people, so we park-hopped.
We go knowing this is how it is and there's no changing it, so we go with the flow and do have a great time. But it makes my head want to explode on other forums/pages when I try to warn people about what to expect so they're not blindsided like we were and others chime in to try and say I'm exaggerating and that October is an amazing time to go to avoid crowds and heat. Nope - crowds roll in and temps stay consistently in the 90s (high 80s, if we're lucky).
I tried to find a picture for you, but the only ones on my phone are of the parade and that always draws a crowd, so it's not the most accurate, since all parades look like that.
Plan for it and you'll have a great trip!