I think people have already made many of the points I would make but just to consolidate and voice them myself:
Guns are just an setting-appropriate art change. They play similar to bows or staves in TQ.
I have no fear that anyone will mistake Grim Dawn for an FPS as it doesn't look even remotely similar. World of Warcraft, Torchlight, and other successful RPGs have featured guns without any problem.
The reload times are not realistic for the era but, then again, I wouldn't say TQ bow attack speed was anywhere near realism either. It is tuned to be fun and balanced.
I'm sorry to hear that some people aren't fond of the addition of guns but, we realize that not everyone is going to like everything we do. At some point though, we have to do something and I think most people have been happy with this direction. For those who aren't, I hope that there will still be enough to like about the game that they can look past the things that may not appeal to their personal sensibilities.