On a couple big projects, I've generally liked it - since there's less boilerplate ("" and closing tags in particular) and the primary identifying bits (- or %ul or .class) are at the far left of each line, I can generally read things more quickly and more easily than e.g. straight HTML or ERB's .
But that comes from rather extended use, I'm definitely not claiming it's the best. There are plenty of things I dislike about HAML, but it does mean I read less, and I spend quite a bit of time reading and writing view code.
Mind if I ask if you've done PHP programming? If you have, ERB's <% would seem to be a tax you've already paid.