I totally agree, the Sigma 35mm f/1.4 | Art is an awesome lens. I've tried the Canon and Nikon mounts and both are super sharp. Can't wait to try out the upcoming Sigma 24-105mm f/4.
The Sigma 35mm certainly gets great reviews everywhere certainly worth considering.
For Milky Way shots I use the 14-24mm it gives you more sky and is just amazing it beats most primes in its range.