Let me start by saying - upgrading to Lion doesn't really bring much else to the table that Snow Leopard offered, in my opinion. In a way, I'm surprised that it's getting such rave reviews. Snow Leopard from Leopard was a far more important upgrade. That said, I'm running Lion on an older MacBook Pro that doesn't feature a multi-touch trackpad, so I can't take full advantage of Lion's new input methods (3-finger swipes, etc.), which is probably its biggest new feature. A touch-friendly interface.
I'm a little surprised by some of Apple's design decisions. Things seem to have been changed for change's sake and none other. Some consistency has been lost, which essentially means there's more inconsistency. And some of the upgraded software actually performs worse than its predecessor without bringing anything new feature-wise to the table.
I expect the performance issues to slowly be dealth with as Lion receives maintenance updates. That's how it always is. However, I'm concerned that some things that have changed are now cemented in and won't be addressed. In a way, I kind of feel helpless, knowing that features that I sorely miss are very low on Apple's priority list. One example is HEX colour support in the DigitalColor Meter. It's now at version 4.0 and has dropped the display of HEX colours. It's also dropped the Edit menu, so I can no longer copy the current colour to my clipboard. Who at Apple thought that was a good idea? It's minor issues like this that have left a sour taste in my mouth. An upgrade is supposed to be an upgrade, not just different for no good reason.
Some of Apple's applications offer built-in feedback forms and I've been using these quite heavily in Safari and Mail. I feel it's important to communicate my thoughts and observations directly to the mother ship, even if the chances that my reported issues being addressed are very slim. Better than not saying anything. Action is always better than standing on the sidelines.
In Mail, they made a very bizarre decision. In the new full-screen mode (new to Lion), when composing an email, the message window is application modal! What's up with that? You can not view other windows, read other emails, or anything. You are stuck. Luckily, this same issue doesn't exist when not in full-screen mode, so I've had to give up that feature to get the behavior that I, not just desire, but need in my workflow.
Speaking of full-screen mode, I like it. I was never a Spaces fan from Leopard and Snow Leopard, I found it confusing. But with Lion, each full-screen app is automatically put into its own space. I no longer need to decide how to organize my spaces, it's done for me. I like that, a lot. It's how it should be, and I'm using full-screen where it makes sense. I was always pleasantly impressed with Google Chrome's implementation of full-screen mode and now Lion is bringing this to every application that chooses to support it.
Launchpad seems like a mostly useless feature for me, although it's been fun to use. It works very well, but seems to have some unnecessary redunancy. You can drag an icon around to reposition it at any time. But you can also go into the "wobble" mode that's available on iOS devices to do the same thing. What's the point of the wobble mode then?
Mission Control is a vast improvement over the various Exposé screen modes in previous Mac OS X versions. It nicely brings everything together, giving direct access to all open applications, the Dock, the Desktop and the Dashboard (the 3 D's). It's very well designed, I think.
I eagerly await updates that address the performance issues, and I hope Apple pays attention to the feedback being sent their way. I encourage everyone to send in any feedback to Apple, no matter how small or seemingly insignificant, because it causes action. It puts pressure on the company that's responsible for this amazing operating system. Without pressure, they will do whatever they want, rather than what we want.
Enjoy your Lion.