I use my S0 for activity/workouts and messages primarily, and I’m quite happy with that but the S0 was really lagging.
Just before going down to Apple, I removed apps I don’t use, but then I actually did a clean install of OS4.
After rebooting the watch, the speed was so improved that, at least for my purposes, I decided that I’m better off waiting for the must-have improvements that come with S4. For now, my S0 may not have Talking Siri or RHR, but it’s doing what I use it for very very well again.