Diablo 1 doesn't support 16/9 and neither does Diablo 2.
I highly recommend Diablo 1 over Diablo 2, they're both really good games that holds up today, but Diablo 1 is different from the other Diablo games. It's way more horror oriented and satanic. Diablo 2 is more gothic though
Thanks for the info. So just 4.3 ratio and what rez? and if I've read correctly you can't play in a window either?
If you are asking about vanilla game, then 4:3 and resolution of 640x480 is what you can expect.
Window mode works perfectly fine on my side.
For "better" resolution there are mods, but they also change the experience, I recommend you to play vanilla game first and then move to mods - some of them are already mentioned in forum, some abandoned (not sure though for some), and some mods are still in development and improving.
For Diablo 2, not bad but some mods are a lot better, but game isn't available here so no point mentioning all those mods out there.