If it's forced enthusiasm, I definitely get annoyed. Like they're this rainbow, happy-colored, no-one-is-supposed-be-this-happy type of person who denies reality in favor of enthusiasm. That really annoys me because it is so forced and fake. If the person is naturally enthusiastic, let's-get-this-done type of person, I don't mind, and I do find it attractive. I myself, like other IxFPs it seems, have some trouble getting excited over things. I prefer to show it, though, than speak it when I do, as I think more people ought to do. (I think that's where my annoyance with over-enthusiastic people comes in.)
It really depends. I generally dislike hyper bubbliness. There is a certain kind of enthusiasm I find wearing. But sometimes I really like it. It's nice to sync excitement with others when it's natural & not coerced. I like when there's a genuine "me too" moment about something you love with someone else.
However, I do resent when people expect me to muster & show feeling over something I don't care about. It doesn't mean I am a grouch; I am simply am not moved. I don't really ask people to be excited for me, so it's not something I readily grasp that others need. It doesn't mean I don't care that they are happy or am trying to devalue it, but I don't feel emotion about it for someone else. It feels strained for me to express anything, then.
If I am genuinely moved or excited, then I will show enthusiasm, but sometimes I still like to go inward with the feeling. When I was younger I was either so content to swim around in my own feeling OR inhibited & mortified of appearing to care, because it felt very vulnerable, that I appeared to not care much at all. But I've gotten more comfortable & natural with expressing emotional responses, and sometimes I muster something so as not to offend.
When I'm really excited about something, I may hasten to be alone with it. If I'm really enthralled it's like everyone around me is blocked out anyway. I'm absorbed with the feeling & it doesn't occur to me to express it in the moment. I think I may have a small smile on my face, because people may notice & ask.
"Charlotte sometimes dreams a wall around herself. But it's always with love - So much love it looks like everything else. Charlotte Sometimes - So far away, glass sealed and pretty." - The Cure
Would you want to describe the excitement it gives?
Because I tend to respond well to excitement rather than being the one starting it. In general. So it gives me something to play from which is fun, and enthusiasm can create a more positive environment to work, create, play in.
Enthusiasm definitely helps me do better work and gives me confidence. When I'm really enthusiastic about something I can run off at the mouth a bit, but most of my friendships are based on shared enthusiasm for our interests and the fact that we all love that enthusiasm in itself.