I love Leopard, its features (Spaces, advanced Exposé features etc) really make my life easier. However I miss Tiger. I dunno why but it just seemed a tad more friendly. It still had the soft corners on the Menu bar, the window theme depended on what app you were running, ShapeShifter still worked and so on.
But you can't get it in store anymore (at least not anywhere in the UK) so I guess those days are gone *sigh*
But yeah. Leopard is awesome. Beats Vista hands down for operability. Now we just need more games published for the Mac.