How it should have ended...
I enjoyed the movie, but John Goodman's acting made him scarier than the aliens. After his death it was hard to build up any tension in the fight in them. If it were my movie I would have...
1. Not had Howard kill Emmett. It solidified him as a bad guy and so much of the tension was from the unsurety.
2. Had Emmett and Michelle both escape together and leave Howard behind.
3. Go into his house (above ground) and learn that there was a reasonable explanation for girl in the photo. Maybe she really was his daughter, or a friend or something to explain what happened. Howard, while an unbalanced survivalist nut, was not evil.
4. As they find out the truth, the aliens make their appearance.
5. The two of them run back to the bunker and try and get in while Howard watches from behind the bunker door in horror and disappointment that they didn't listen. He can only stare as two of them are killed by the aliens, leaving him alone and the only survivor. Forever alone in his bunker.