: If you want to try before you buy, fansites like SeriousSite.ru sometimes host official demos for various Serious Sam titles.
While you might be looking for a "free download," the game is a commercial title. It is frequently available for a very low price (often under $5) on major digital storefronts: Serious Sam: The Random Encounter Free Download
It sounds like you're looking for a short essay or overview of the game , perhaps while searching for a way to play it. Mini-Essay: Subverting the Chaos : If you want to try before you