I'm a bit disappointed. Leopard cost £85 in the UK ($170) for single licence, whereas Tiger and Panther cost only £69 even when the US exchange rate was worse.
Stacks look nice but they actually lose functionailty over the previous folder-in-dock arrangement. In previous versions, dragging a folder into the dock full of application aliases for example would enable a stacked 'Windows Start Menu' by holding down the button. You could delve deep into folders contained within via stacked menus. But now, folders within a stack are ironically not stacked, meaning a laborious opening of the finder is now neccessary. Plus, a fan view stack can only display 7 items before displaying the 'more in Finder' menu. Style over function or useability. Sigh.
It's nice that the Finder is now a Cocoa app (finally!), but the view behaviour can be a little odd. For example, in the simple view, you can set your Mac HD to always view as simple icon view but, e.g. if you keep your default view as cover flow, then any further generated windows will be in cover flow, with no easy option to change view. Cover Flow looks nice but its useability is pretty rubbish (being a very slow way to navigate), and unnecessary in my view seeing as quick look functions well.
The number of usability changes from Tiger staggers me, and will cause much confusion for lots of users. Doubly bad if you are caught without internet, as I was this weekend, as the help system is completely online only. Spotlight has changed - if you click on the 'show all' it goes to a Finder window, not the previous Tiger window with many options.
But the worst culpit is the new window appearance. Apple has seemingly consigned the Aqua and its pinstripes to the graveyard, preferring a drab grey instead. It has also increased the depth of drop shadows to give windows a more 3D and cartoony look. However, in doing so, inactive windows now appear pretty much exactly like active windows did in Tiger, which could be confusing. This came up before, when inactive Panther windows looked similar to active Jaguar windows (althuogh Panther introduced more subtle pinstripes and so the effect was less marked than in Leopard). Interestingly, iTunes doesn't support the new unified interface.
My Mac doesn't even support the fake transparency in the menu bar (preferring a drab grey that looks like Mac OS 9 instead), even though all other effects are fast and supported.
There are lots of things I like about Leopard, but there are some annoyances as well.