And so... I've been using Mac OS X "El Capitan" Public Beta for a full day now.

Not terribly impressed. Some things I've observed in the past 16 hours...

• First the crap news. Apple STILL hasn't given users an option to have the menu bar persist in full-screen apps. And I just don't get it. I would love to be able to work in full-screen. But I need the information in my menu bar. Like the clock, for instance. Like the battery level, for instance. Like my VPN status, for instance. Like my calendar, for instance. — But here's the weird thing. Apple has added a new feature which does exactly the opposite. You now have the option for hiding the menu bar when not in full-screen! WHAT THE FUCK?!?? WHY?!??
• Visually, there's very little difference between Yosemite and El Capitan. The Spinning Beach Ball of Death is no longer gum-drop looking, but instead flattened out... and the system font has been changed a bit (for the better)... but that's about all I can see.
• One of the major things Apple is touting for El Capitan is an overall speed increase. App switching twice as fast... Two times faster display of first message in Mail... Four times faster PDF display... etc. etc. I don't really notice such drastic increases, but I'll take Apple at their word. Unfortunately, this speed bump seems to be coming at a price. The fan on my MacBook Pro keeps coming on. In Yosemite, it rarely did. I don't know if this is a direct result of El Capitan... or perhaps one of my background apps (like anti-virus or DropBox or whatever) not being optimized for El Capitan. Hoping eventually it will get sorted out, because the fan noise is annoying.
• I have found two incompatible apps so far. Fantastical 2 (download the beta for El Capitan), and SpanSieve (join the beta program to get a compatible version).
• I am a Spaces super-user. If I ever had to go back to a Mac without virtual desktops, I'd go insane. There has been some changes to both "Spaces" and it's parent app "Mission Control"... that I guess are good moves. I don't like that you no longer see tiny representations of your Spaces any more until you mouse over them... just text saying "Desktop 1," "Desktop 2," etc. but it's not a deal breaker. Just makes it more difficult to remember where you put things.
• Speaking of Spaces, Apple has now set "Dashboard" (their widget screen) OFF by default. I can only guess this means Dashboard is not long for this world, which fucking sucks. I set up Dashboard in my first Spaces slot and use it constantly.
• Apple has added the option to do split-screen apps, but it's implementation is total shit. Press and hold on the green "stoplight" control in the menu bar and you can drop the app window on the left or right side of your display. In the case of Mail, the window just gets resized. In the case of Safari, the window is scaled. No, I have no idea why there's a difference. But here's where Apple shits the bed... the apps appear to be considered "full screen" when in their split-screen region. Since the menu bar is now both split AND hidden, things get messy very quickly. Apple apps are consistently screwed up this way, but with NON-Apple apps, it's so much worse. Go split-screen with Acrobat Pro and you lose the menu bar entirely! And the disasters don't stop there. Sometimes you can't get out of split-screen. Sometimes you go from split-screen to full-screen for no reason. Sometimes windows go inactive when in split-screen. And as if ALL THAT wasn't enough... you can't use split-screen across Spaces! The two windows you want to go split-screen have to be in the same Space! Insanity. The hits go on and on. I guess this might be a nice feature once the bugs are ironed out, but I'll probably stick with Moom for Window management.
• Mail has a bunch of improvements... like tabs for composing multiple emails and gestures taken from iOS, which is nice. Being able to two-finger swipe on an email to rapidly trash a bunch of spam is sweet. But the one thing I really wanted for Mail didn't happen. A previous version of mail took away the user's ability to pick which SMTP server to use to send your message on the fly. This was a critical feature for me when traveling, and I'm pretty desperate to have it back. Nope. I understand wanting to simplify mail for people who don't need things like this... but come on. Give the people who need it the option to turn it on. Removing features like this is a big fuck-you from the "We Know What's Best for You" mentality at Apple. WARNING: For reasons unknown, I lost all my Mail account passwords after installing El Capitan. Luckily, I was able to get them out of Keychain on my office Mac since everything is synced (who remembers passwords anymore?) or else I'd be boned and have to change everything.
• Apple's system-wide search tool, Spotlight, has always been a pile of shit. In trying to make things simple, Apple just made it harder to use, so I pretty much never use it. With El Capitan, Apple has added a bunch of new capabilities and features to Spotlight... use natural language for requests... get limited info from the internet like weather and sports scores... that kind of stuff. If possible, I hate spotlight even more now. It's just a big fucking mess and a huge distraction. Thank heavens for third-party solutions that actually do search right (EasyFind, Alfred, Tembo, HoudahSpot, etc.).

A lot of things I'd liked fixed/changed, to be sure. But the biggest is my laptop fan going off and on all day long. It just sucks to have to listen to it all the time when I rarely had to with previous OS X versions. If this is the cost for speed bumps I barely notice, then no thanks. Hopefully Apple is on the case.

UPDATE: After futzing around with the CPU monitor, I think that it's Mail that's the culprit. Even when running in the background, it's pegged at 138%+ CPU usage. Quitting Mail lets my laptop run much, much cooler. Guess I might be needing to find a new app for email.