Not enough enhancements over the original game is not a problem because this is a REMAKE with new graphics! that's all!
I think developers have tried to remake the original game exactly as it was with modern visuals. Gamespot says "Not enough enhancements over the original game, making it seem kind of unnecessary" . Actually I can see a huge enhancement in graphics. And that's the one and only thing they can enhance without harming the feel of the original game. I think they have done a great job. Same story , same menus, same music and sound effects but with new graphics. So we can re play the original Serious Sam First Encounter!
Actually they do not need to enhance the content of this remake to feel us better.In order to do that they are developing Serious Sam 3. So we can get a completely new experience. If Serious Sam 3 came out without much enhancements we can blame on developers for sure. But a remake is meant to be a remake which reminds us the original! It should give us the same feeling , not a new feeling.So I think Serious Sam HD First Encounter did that job well....