Well, Panther had the one major feature that brought me to the Mac -- Expose! Dashboard is a nice gee-whiz kind of thing, but Expose is a serious usability tool (rather than a floating collection of simple utilities). Now Spotlight... that's another serious usability tool but after 10 years of working with hierarchical folders, it's going to take me some time to get used to being able to put files anyplace and still bring them up in one or two keystrokes.
Burn Folders are VERY nice -- a feature I've long missed from my old days as an OS/2 user on the PC before I turned to the dark side with Windows and before I bought my first Mac last year).
But yeah, Panther's a great system. I would have still been using Panther if not for the $35 Tiger rebate from Amazon. $94 is a decent price for an upgrade. $129 is not.