will there be any compatibility issues with win 8 with gog games?

Windows 8 is generally _expected_ to be pretty compatible in this regard. Most games will probably not require any adjustments. Some GOGgers are already using the Win8 beta, and the games with problems seem to be exceptions.

GOG has stated (at the conference streamed some days ago) that they plan to make their games Win8 compatible (if they aren't already), but that they want to wait a bit before Win8 has settled down a bit, and has seen its first service pack.