Hi Guillermo. Nice to meet you. I know your game from the TIGSource forum :) I must say your game look totally great! I have two questions to you:
1) Did you play the Serious Sam #1 or #2? And if yes, are you inspired by this game in any way?
2) How do you feel with developing it in Unity3D? Do you like this engine or maybe you wish you did another choice in the past?
We are developing our game in Unity3D too and generally we love this engine but the worst part of the all development tools is the Visual Studio (MonoDevelop too).
Good luck with your game! We are following you :)