pcmag seems to like the 10.5.2 update. a lot. Apple OS X 10.5.2 (Leopard) - Reviews by PC Magazine
my favorite features are the small ones - quicklook, the mosaic screensaver, and the dedicated downloads folder (though i made my own in every past version).
i do not like the removal of the bluetooth phone pairing w/address book that allowed you to send text messages from your phone via your computer...there's a company that sells a hack to enable this, but i don't know why apple removed it. still, 10.5.2 fixed a lot of silly things that apple got wrong in the original release.