What a gift to see such a well-established product. Seth Godin uses this for his famous blog - what more do you need to know?
The design has been commented on and I must say that I take a UX that has come (only very slightly) of age over "glossy but buggy" every day!
The features are well thought out which shows years (dare I say decades) of development work and listening to customers (something that fresh products simply cannot offer).
Limits are generous! And it is not just about subscriber counts! Unlimited channels/lists... get outta here LOL! If you have different products (or courses in our case) you can let users subscribe (and unsubscribe) to them separately. (Note that this is very different from tagging - which FB also has, of course.)
We did upgrade to custom domain which is offered at a very reasonable price and was a pleasure to pay a handful of $ for such a complete package.
I also love the clever template system.
We are < 24 hours into this, so still discovering many features - but the deep first impression is rock solid!