When I don't want every single message to hit my inbox, I need rules. This was important for me when I had e-mail being pushed to my phone along with being accessed online.

And one particular need I had that GMail couldn't do was the ability to apply a label, skip the inbox, but only if my exact e-mail address wasn't in the To or Cc fields. i.e., a message sent to a list should always have a label and skip the inbox. However, if I was also directly sent the message, I wanted it in the inbox.

I wouldn't complain much about this limitation if it was my personal free account, since I'm just the product being sold in that case. However, this limitation did hinder me when I actually was a customer, as part of a company paying them for hosted corporate e-mail. To me, it's a failure if your paid for, commercial service aimed even at enterprise can't match the features of the competitors in the space. Especially when one of those competitors is Microsoft with Exchange.

I do see GMail as being a decent webmail experience, and acceptable for a majority of users out there. Though much like Tony C, I prefer a native client. The rise of the modern free web clients came after I had already migrated to IMAP, and server side filtering, so none of it was particularly novel to me either. Prior to that, I did use a mix of local and webmail, with one of the first free webmail providers out there, USA.net (I worked for their sister company for a bit).