Three things I'd like to suggest:

1. You should be able to limit download speed
2. Show time remaining til download is complete.
3. It would be nice if you could minimize it.

I know someone mentioned before about having a throttle for the download rate. Issue is I've never seen something that, the closest I've seen was the resource usage option on my virus scanner. That's not to say it doesn't exist though.

The time till completion thing shouldn't be much of an issue since your typical download by browser does that, though that number is indefinitely changeable depending on everything from your network server speed to throttling by your internet supplier to resources the computer is using. Some people might also find it invasive if it does read all of that.

I just discovered that the downloader can be minimized if you click the "X" which usually means close. I would still like three separate buttons though; minimize, maximize and close.

The problem with download speed is that if your connection is maxed out you cannot do other things on the internet until the download is completed.

You are right that almost all browsers shows time remaining so I just don't understand why it isn't included here :)

Use the wishlist or write your suggestions in GOG.com downloader beta thread:
http://www.gog.com/en/forum/general/page3#1334932702

Many applications treat the X icon as "minimize to tray" and the other icon as "minimize to taskbar" so I don't see any reason why the GOG downloader should do that differently. I'm rather concerned about issues with downloads occasionally stopping for no reason or causing the .NET framework to crash (although I have no idea how many users experience these problems).

I agree though that the downloader should display the time reamining until the download is finished, especially since it's a very simple calculation and it should be a matter of minutes to add this feature to the tool.