This name sounds very 'Lord of the Rings' to me - and that's a good thing! I've found that I get that impression from a lot of Welsh names. This name is really pretty, and I love the meaning.
I'd never really heard of this name before, until I started college last year, and there was a girl in my group called Eirlys. I think it's quite a nice name altogether, but in the case of the girl in college, everybody kept mispronouncing her name, and she is forever cursed with having to correct people, because people keep calling her Iris. I've come to the conclusion that it must be rare, even in Wales, because even though it's Welsh, I've never really heard it, and I'm Welsh.
Beautiful name with a beautiful meaning! I absolutely love this name. When I have a kid in the future, I'll either use this name or alter it a little...maybe something like "Irlyssa" or "Irelysse."