For me it depends on the characteristics of the party, such as what the people are like. I hate it when it seems impossible to find anybody to talk with, where there's just a sea of people with their backs to me obeying some obscure social rules, I can't seem to break into that kind of thing and I feel very bored and self-conscious if I'm being ignored. Sometimes I can do a bit of one-on-one, but I can't keep it going very long. I hate being expected to stand about holding a drink in one hand and a plate of food in the other, it's so uncomfortable. Then they might have loud music I don't like, or dancing which I can't do or relate to (except maybe at a ceilidh if I had a chance to practice a bit beforehand). It's often very crowded too, and too much background noise. I never had a meltdown at such an event, but I used to get drunk out of boredom and do stupid things, unfortunately they weren't the same stupid things that everybody else there would be doing.
On the other hand, small, quiet soirees conducted with dignity, plenty of comfy chairs, a tea and coffee option, vegetarian food, no queue for the toilet, and noncompetitive people with a good sense of inclusionism, that kind of thing can work really well for me. Luckily as one gets older, parties tend to get more like that.