If you're a hardcore Apple nerd, you've probably already bought and started installing Mountain Lion. For the rest of you, here's a collection of reviews that I'll be reading once I have a chance, roughly in this order, that might help in your decision of whether to upgrade:
John Siracusa's epic 24 page review on Arstechnica
The most in-depth review you could possibly find of Mountain Lion.
But hang on a second. For a desktop OS in the year 2012, which direction is "forward," anyway? The obvious answer is "toward iOS," but Lion proved that it's not quite that simple. And really, there has to be more to it than compulsive imitation, otherwise why continue development of the Mac platform at all?
Mountain Lion is Apple's answer to all these questions. It is the digital manifestation of Apple's belief that the Mac is still relevant, that it can be made better than it was before. In some ways, I feel the same as I did over a decade ago when considering a new version of OS X: I want to believe.
Related: Read Marco Arment's review of John Siracuas's review if you want some truly meta-review level reviews in your head.
The 10.8 review maintains Siracusa’s standard at approximately 26,000 words, an impressive feat given that the interval between 10.7 and 10.8 was much shorter than most previous OS X update intervals.
John Gruber's Review on Daring Fireball
But Mountain Lion isn’t billed as a blockbuster release, and it isn’t priced like one. It’s just nicer. And it’s the little things, the attention to detail, that show it best. I’ve spent most of my time testing Mountain Lion on a 2010 11-inch MacBook Air. I’ve noticed that wake-from-sleep times have gotten faster over the course of the beta period. And the MacBook Air woke from sleep just fine on Lion, by the historical standards of Apple notebooks waking from sleep. But “faster” isn’t fast enough, and the Air now feels like it’s getting pretty close to the instant-on wake-from-sleep feel of an iOS device.
Shaun Blanc's Review, Titled 'Mountain Lion and the Simplification of OS X'
iOS is both the learning ground and the excuse for the simplification of OS X.
TUAW's Review
I am not going to attempt to exhaustively work my way through all two hundred plus features and write in detail about each and every one. The plan is to hit the highlights, tell you what's changed, and let you know why that's a good thing -- unless it isn't. In which case, I'll tell you why not. Think of this as the amuse-bouche to Ars Technica and John Siracusa's no-expense-spared tasting menu.
Send them all to your Instapaper cue for reading.