I admit Gmail's web interface is a bit weak. However, it's feature capabilities are incredibly powerful.
Most email clients can't seem to get a
simple keyword search to work correctly. What the hell is up with that? Google's keywords search works perfectly, and the advanced search is incredible. If you didn't know about it:
https://support.google.com/mail/answer/7190?hl=en
At a time when most email providers had paltry size limits, Gmail gave us gigabytes of storage for free. And it's ever increasing.
I love the filters and actions that do automatic routing into separate "labels" (folders), or even the trash can.
The spam detection is vastly superior to Hotmail. I get Hotmail spam almost every single day. I get spam in gmail about once every 3-4 months.
You don't HAVE TO use Gmail's web UI. Use any client you want.
Also, Gmail is the only back end that works with my favorite iOS email client, Mailbox. Mailbox has a very clean UI and uses simple gesture-based commands to quickly accomplish typical tasks. No need to have have buttons all over the place or to first have to tap-to-reveal the buttons.
I think of Gmail as being similar to Excel. It's not very pretty, but it's got power and it gets the job done in a way that nobody else can quite match.