It's been almost 6 months that I have been working on Lightning Full Time and here are my thoughts:

• Lightning is a far superior platform than classic
• We should all be working towards having reusable development and componentized (is this a word?) pages across all applications including mobile.
• Lightning allows admins and devs to work closer together to meet a requirement.  Just because your page requires a custom component doesn't mean your whole page has to be custom which used to be the case for most VF Pages. 
• The ability to have dynamic pages based on criteria makes it much easier to manage UX for different user types rather than having to manage a page for each user type/profile
• The LEX on Mobile pilot is the most important pilot salesforce has put out in a long time (this is just my opinion as someone who is heavy into mobile app dev).
• All teams at salesforce should strive to be as transparent with their roadmap the lightning team is with theirs. 
• The Trailhead sample gallery gives great ideas for look and feel of pages.
• Admins have quite a bit more options from a configuration standpoint which also makes us more UX Designer and less having to live within constraints of a platform.
• Lightning Components are the best invention since custom metadata types.  Or maybe components came later, not sure, but I can't imagine my life without them.  I have a massive org without a single VF page.
• Not once in classic was I ever really able to blow people's minds.  My greatest joy is blowing the minds of Lightning and Mobile PM's with the apps I work on/design.
• I'm excited for Lightning web components.

There are three things I switch back to classic for:

1. Logging in as another user - this seems to have gotten somewhat better in lightning but still not perfect
2. Recycle bin - I think this coming
3. Reporting - sorry @Liz Skaates I have a hard time with reports in lightning.  I feel like I get lost in them.  I end up switching back to classic and can create reports like boom boom boom done.  I'm working on it.  I don't think this is a salesforce thing, but a cheryl thing.  An old dog can only learn so many new tricks.