Any Serious Sam is good Serious Sam as far as I'm concerned. SS2 was... very different... But I did still enjoy it and it did still have that whacky sense of humor that Croteam is famous for.
I would however prefer a return to Egypt and the same style of gameplay as the first games had. Simple is often better in these situations. Remake the first game on a brand new engine with a little more 'depth' to the puzzles and environment... Serious Sam Redux?