Serious Sam wasn't all about blowing lot's of stuff up.
It had the pacing and suspenseful moments of a good movie, something many games either don't bother with or simply fail at. They usually involve monsters spawning after obtaining a powerful item, or creepy ambience prior to a big battle. The occasional tongue-in-cheek humor was another rarity. There were even moments when I empathized with that flippant little computer in Sam's head.
The Second Encounter added several memorable setpieces. Such as that cylindrical room where the laws of physics need not apply and the large field of that last great battle which starts out bright and refreshing but darkens into thunder and lightning as monsters flood into it.
SS was DOOM liberated from id's techno-gothic restraints.
"Nothing livens up a robotic hymn of doom more than an amazing pair of jugs." - Brak