I like how easy it is, because you can set up rules in minutes! It's very customizable so that we're able keep our processes fresh with new features as they come out or if someone needs something different than what comes builtin by default (like custom fields).
There are some quirks here & there but nothing major at this point - just be open minded about things when setting them initially :) We've been using their service since 2013 without issue until now where one day all my contacts were suddenly not showing within any channels after logging back online from being away during lunch time. For me personally its solved most issues i had previously having multiple inbox managers who would forget which emails got sent/received etc.