It's been quite a while since I've seen a (IMHO) great movie. I've seen quite a few good ones, and a reasonable number of very good ones over the last couple years. (I don't get the opportunity to go very often, so I'm pretty careful to only see ones with good reviews from critics I trust.) But a great movie only seems to come along every two or three years at best.
Once is a great movie. It made me feel deeply as only a great movie can do. The music is spectacular. (The first thing I did when I got back to my computer was order the soundtrack.)
If you can go see it, then don't miss it.