I hate to be cynical, but you did ask for feedback, so here goes!
View attachment 1853
I know that's there for debug purposes, but it could throw people off if they've never used the launcher before. Consider building release builds for the public to use and putting the messagebox around a pre-processor directive (i.e. #if DEBUG).
View attachment 1855
Again - I know this is an open
beta, but is there no way you could display this in MB/GB? And maybe a speed too?
View attachment 1856
I'm not trying to cause some sort of graphics war here, but the background here certainly looks bleak and colourless. Why did you choose this? We can't see the chat behind it, so why not choose a screenshot with more colour? It looks very uninteresting to the point where it's almost boring; why did you go for something that's in the background of the first "screen" - make it more diverse!
There's also this annoying flickering on the item that is being installed/downloaded. Can't really show that here though.
I do like the custom progressbars though, and the launcher works nicely - it installed TSO quickly along with all the prerequisites!