My lung capacity has increased a great deal. I blew out all the candles on my 58th birthday cake, and I couldn't get halfway through my 54th.
My doctor found my blood oxygen level after six months vaping to be the same as if I had never smoked.
The hacking cough from smoking for years disappeared within the first three months.
The occasional cold is now just a cold for a couple days, without bronchitis or inflamed lungs.
The only negative side effects I've had are the need to keep hydrated and an occasionally scratchy throat. In the winter months when it's drier, I use less flavoring to help my throat out.
Overall, my better health is well worth a few extra glasses of water a day.