Agreed! It had great functionality, including customizabiltit and the best approach to separating wheat from chaff I've seen to date. Spark is entirely client side (Though they're hinting at adding server-side features; as long as it doesn't include server-side access to my email no problem).

Mac client slated for early 2016. They support plain IMAP (yes!) and even Exchange.

Spark and Outlook seem to be the most delightful to use.

I'm quite happy with Spark, been using it the last few months. I got tired of Gmail's webapp app.