At first I didn't like it, but the more I think about it, the more I do. First of all, I think the name is important - Apple is pushing the names of their releases. Since Mavericks, you can see the name during install and in 'About this Mac' and in the App Store as well. No one calls Yosemite "10.10", everyone calls it Yosemite - as far as I know, anyway. Now, when I first heard El Capitan, I thought it was a joke. But now? It's a good name. Why? Because it's different. It sticks. It's somehow unique exactly because it doesn't sound like a fantasy name for little boys. No, they don't have to name it "Snow Leopard, or Death Valley, or Dragon" for it to be a good name.
It is the spanish version of an Indian word, meaning chieftain. That alone makes it cool!
Also - OS X El Capitan is great. The DP version is really fast and stable - just what I wanted. And I just love the new Mission Control and Split View. They might seem like little features, but for me, they actually changed how I use my Macs! And that's even before we get into Metal, which has potential to be a gamechanger. So, with all that - the name El Capitan somehow fills me with joy!