Well, there are broken things that are bugs and then things that are broken by design.

By design you have things like the atrocious menu bar, dock, stacks' overlapped icons in the dock, dock's inability to show folder contents as a list, super-fugly folder icons, no way to set file ownership from GUI anymore, the nice rounded corners on the menu bar are gone, the blue apple top left is now black, help viewer is now some bastard always-on-top non-standard window that can't be closed from the keyboard, throbbers in Mail spin way too fast, Time Machine asks if it can use every single external volume you connect and there's no way to disable this pain in the ass prompting from the GUI even if Time Machine is OFF, etc...

Things that are broken with bugs include, lots of crashes in Mail even when it's just sitting there doing nothing, lots of crashes in Safari without hitting bad pages, crashes when hitting bad pages, safari gets frozen/bogged often while working on one page that it affects all windows and/or tabs, ownership issues when updating from Tiger due to missing user group causes an "unknown" group to appear in file perms, adjusting ACL/perms can crash because of this, finder unable to eject DVD from drive quite often with keyboard shortcut (drag to trash usually works), unable to eject some external volumes every now and then, shared computers sometimes don't show their folders and are unable to be ejected/refreshed, spotlight completely trashes and permanently damages Tiger's Spotlight on another drive, renaming a file inside an expanded subfolder while in list view will escape out of rename if you hold the left cursor key to try and move the insertion point, connecting and/or disconnecting an external display to my PowerBook will often leave the graphics rendering in some weird state that looks like 16bit without dithering, doing the same can often leave font smoothing in some weird state where some fonts on some web pages now look much thinner than they're supposed to, these last two issues can affect the external display, internal or both (ATI graphics on this machine), on my Intel Mac PubSubAgent crashes every 10 minutes and all text/string objects in iTunes windows appear inside a light grey box instead of properly showing through to the window background, etc...

On the plus side, WiFi reception seems to be much better. I tested this by switching between Tiger and Leopard without changing anything else nor moving the machine. It was a huge surprise to say the least.

The folder icons are fugly and not on an angle for only one reason - so they show up properly in Cover Flow. They should have included an alternate icon resource that could be used for CoverFlow views. This would solve a lot of problems with a lot of file types. Strangely I've never seen anyone else mention this as the reason for the new icons.

Apple knew Leopard wasn't ready for prime time when they released it. But there's no way they were going to pull a Vista again.

The examples I mentioned above are strictly issues that I have right now or have had with my two Leopard installations. I'm not including the enormous list of problems other people have had with things like Time Machine, Spaces and other features, nor am I including the issues caused to third-party programs (and many not because those programs were at all deficient or bending the rules).

The 10.5.2 update is going to be enormous in size and is the version that I've always heard one should wait for before updating to Leopard (I first heard this back in early October from friends that work closely with Apple).