It's interesting to hear Angel Beats was a first for a lot of people.
For me my whole thing was -> Grave of the Fireflies (first movie, love this movie a lot still) -> FMA (first series)
But the first anime that made me passionately fall in love with anime was Baccano, funnily. It was probably one of my first 10 or so anime. It was something where I saw the poster and I thought, this looks like something I'll love. And I was right.
It's funny, when I reflect on my top 100 anime, most things in it are definitely from earlier in my anime watching time period. So I'm like 'am I more cynical now?' Probably partially, but I think it's also that things that appeal to you exist less and less as you finish off series.