Here's the pros and cons from my experience. I don't use Apple Mail so I can't comment on that.
Catalina features:
• Dark mode
• Reminders compatible with iOS 13 Reminders
Catalina woes:
• Display issues galore
• Installation issues
• Remote app for iOS incompatible
• Problems with exporting bold fonts to .pdf
• Kernel panics (mine possibly resolved by unplugging ext. DVD-RW)
• Loss of some iTunes artwork
• User customized views in iTunes gone in Music app. Not surprising, but wish I'd have taken screenshots of my iTunes views
• 32 bit app incompatibility
• Sidebar favorites disappeared. Had to re-add them
• Major app issues with Photoshop CC: RAW editing in ACR barely functional, 'Save As' loses file type suffix
• Loss of many folder icons. Now appearing as document icons
In summary, wait a month or two for stuff to get updated. I don't want the installation woes of going back to Mojave, then back again to Catalina so I'm weathering the storm for a few months.