Leopard is great. I had it when it was 10.5.1. I went to back to Tiger 2 weeks later because of too many "minor inconveniences." 2 weeks after I was back on Tiger, 10.5.2 came out, so I tried Leopard again. I have since been using it for almost 2 months now. It's very good.
There are things I still liked about Tiger, though. The new features in Leopard make it worth the upgrade, though. I love the Time Machine. I love the calculator and dictionary built into Spotlight. I love Spaces (even though it's inferior to Linux's Workspaces). I love being able to F around with my Dock (3rd party software). I love how it's faster all around. And I love the little things like iCal's Dock icon showing the actual date, even when it's closed.
I kinda miss Tiger's Sidebar, though; I think Tiger's was much superior.