It's not a mail client at all just the System Preferences screen for Mail, Contacts & Calendars in Lion. I can say that Mail in 10.7 is an excellent alternative to any client you may be using at the moment.
While I respect your opinion, I disagree. Sometime after it's launch and there is an upgrade I think Mail will be more of a contender. However from what I've seen and experienced thus far Gmail is still far better.
iCloud in it's entirety is Apples effort to catch up to Google. They've got a way to go yet. The level of refinement, constant improvement and consistent performance I've enjoyed with Gmail is untouched by any competitor to date.
While I believe that Apple certainly has the resources to compete, they've proven over and over that online services are not their area of expertise. I've used MobileMe since day one, and still use it today. But only because I'm a true Apple supporter and being patient while they find their way.
I do hope that Apple gets it right with iCloud, but I have no confidence it will come out of the gate the right way on day one.