I made the switch from the OG PW to the PW2. I don't think I'd have done it without the sale Best Buy had ($50 off) and giving me $80 credit for my older watch (which was increased to $110 when Google offered that).
The battery life is noticeably increased from the original. With Always-On Display, I can still get about 36 hours before having to charge it.
The watch seems snappier as well, maybe due to the new processor?
I am disappointed that I can't take advantage of the irregular heart notifications. Apparently if you've been diagnosed with afib (which I was on my OG PW), you aren't eligible for that feature.
Overall though, I'm pretty pleased with my purchase.