Rims are a little weak, but the obverse detail is strong. Surfaces look a little porous and the date is a little weak but full. So it has a few negatives, but I think it could safely be called a Good-4.
I didn't research it but going from memory, that seems to have a great deal more detail than slabbed examples in G04, on the obverse at least. Cool find!
Yes G-4 is an excellent rating for the coin's condition. I like the overprint on these Buffalos because it can be seen with the naked eye. Nothing aggravates me more than doubling or re-punched mint marks when you have to break out your X10 loupe in order to even see it. Nice purchase.