PC.IGN.COM reports that Serious Sam 3, is apparently far into development and scheduled for release in 2003. Here is a clip:

The new game, Serious Sam 2, ironically now possibly referred to either factually or mistakenly by reps as Serious Sam 3, is apparently far into development and scheduled to hit in 2003, completely compatible with the Xbox's own Live multiplayer setup. Even fewer details are known of the PC version, but assumedly it is in concurrent development, since musings of that one have been around since well before the Second Encounter even hit.