But the review that programmers were waiting for was the one by fellow developer John Siracusa, the Ars Technica columnist who wrote the definitive assessments of the previous five versions of OS X — and has been described as the guy who should be in charge of Finder development at Apple.

Siracusa took careful notes at the Apple developers conferences and has been living with Leopard since the first seed was released. His review came out on Sunday, and it’s a doozy — long, deep, painstaking detailed, and unafraid to call ’em like he sees ’em.

He lays out his criteria right at the top:

And as I see it, operating system beauty is more than skin deep. While the casual Mac user will gauge Leopard’s worth by reading about the marquee features or watching a guided tour movie at Apple’s web site, those of us with an unhealthy obsession with operating systems will be trolling through the internals to see what’s really changed.

These two views of Leopard, the interface and the internals, lead to two very different assessments. Somewhere in between lie the features themselves, judged not by the technology they’re based on or the interface provided for them, but by what they can actually do for the user. (link)

True to his word, Siracusa gives us two reviews — a user’s view of the look and feel of the OS and a developer’s view of the stuff going on under the hood.

The stuff under the hood gets high marks. The terms that come up over and over are “sensible,” “pragmatic” and “compromise.” A typical summary graph:

The minimal, almost humble way Core Animation integrates with Cocoa belies its incredible sophistication. More so than any other new framework in Leopard, Core Animation provides functionality and performance that was previously difficult or impossible for the average Cocoa programmer to create on his own. Now, finally, third-party applications can look as impressive as Apple’s, and they can do so by using exactly the same code that Apple’s using—code written by expert graphics programmers and continually revised and improved by Apple to take advantage of the latest hardware. Excellent.

About the hood itself, he’s not so kind. A hard taskmaster when it comes to user interfaces, Siracusa faults Apple again and again for choosing flash over usability. He sums up the problem — and speculates about its source — in two damning paragraphs:

Leopard’s new look has been compared to the Aero Glass look in Windows Vista. While I think there are few legitimate similarities, this comparison comes up as often as it does because the two designs share one prominent attribute: the gratuitous, inappropriate use of translucency to the detriment of usability.

Why, Apple? Why!? Was there something horribly wrong with the existing menu bar—something that could only be fixed by injuring its legibility? Like the folder icons and the Dock, it’s not so much a fatal flaw in and of itself. It’s what it implies about the situation at Apple that is so troubling. What in the holy hell has to happen in a meeting for this idea to get the green light? Is this the dark side of Steve Jobs’s iron-fisted rule—that there’s always a risk that an obviously ridiculous and horrible idea will be expressed in his presence and he’ll (inexplicably) latch onto it and make it happen? Ugh, I don’t even want to think about it.

Even if you never wrote or hope to write a line of code, you’ll learn a lot about Apple, its operating systems and the future of Macintosh applications from reading Siracusa. Highly recommended.