They are basically big guys with super guns and an enormous amount of health. All you can do is pull out your biggest gun and hold down the trigger. Another unique part of Serious Sam is its multiplayer. In this area, the game revisits a technique that hasn't been used for 1st person games in quite a while. In addition to the standard deathmatch and team deathmatch games, there is also the option for a co-op mode that lets you play through the entire campaign.
Deathmatch mode is also good, although only one map is made available with the game.
Thankfully, the game also includes a custom level designer so finding or creating extra maps should not be a problem. Serious Sam's best friend may also be its worst enemy. It is also somewhat formulaic in that the only challenge is to kill things and get to the other side of the map. As you progress you get exceedingly large guns which give way to even larger guns as you advance further. In my opinion, this game's saving grace is its co-op multiplayer option.