What a beautiful day! or
What a jerk!. The phrase doesn't have in general any positive or negative connotation, but is just a general exclamation about the perceived (large) magnitude of something, good or bad. (
What a generous offer!,
What a terrible surprise!)
Of course one could also use any of the above sarcastically, inverting the meanings.
Anyway, my guess is that one might say something like
(Вот) так красивый день! or
(Вот) такой красивый день! in Russian to mean something similar, but really I have no idea.