Miljac: Being optional and non intrusive is the way to go. Some say you should leave checkbox to install it unchecked by default, and that would be much better. But even better (my personal opinion) would be if you only included download link to galaxy. That way, you will not bloat installer with galaxy client.
Johny.: I'm just a member of Galaxy Client development team (formerly website team) and I don't think I can answer most of your concerns.
About including Galaxy Client installer - yeah, including all of it in the game installer is probably not the most optimized solution.
I think it's nice for it to be seamless, so it wouldn't require new users to click the link, download and install manually, but simply have a checkbox for that.
It would be really nice to have (optional to run) galaxy-client-downloading functionality in the game installers instead of having Galaxy Client installer embedded there. We'll see how that turns out in the future. The advantage here is having it working totally offline.
Johny, the problem with including the Galaxy client in the installer is that you're not impacting new users - you're mostly impacting existing users who are already opting out of using Galaxy.
There's no point to installing client software offline, the whole point of clients is that they manage updates and multiplayer, social connections, shopping, etc. All of that depends on internet connectivity. So the goal of 'completely offline installation of client' is just nonsense.
Anyone who is completely offline is already going out of their way to avoid game clients in general; now you and GOG are trying to trick them into installing a client they don't want and won't provide anything useful for them. Do you see why people are so upset and why this change is not wanted?
This is scummy. It's what I expect from toolbar developers, not a company that I've trusted for several years.