As much as I liked The First Encounter, The Second Encounter is where it's at. Old school 3D shooter fun (not as old school as DOOM, of course) at its best.
There's a difficulty for everyone. At the lowest setting, nobody should have a problem. At the highest setting, for the hardcore gamer in you, the game is still playable and tons of fun with hundreds if not thousands of enemies coming at you, all with their particular appearance, warning sound effect, powers and personality.
You will rush for health and bullets, but always feel like you can overcome the odds and feel like a superhuman at the end of the day.
The environments are more varied and beautiful than in the first game, there's more humor and even the freaking secrets are fun this time around.