Damn, I only made it two days.

I think I need to spend more time on the barricade.

Don't over-repair. Search for survivors first, then weapons. Survivors help you shoot, and help you repair. Once you've got about 5 survivors, focus on weapons searching (say 70/30 or 50/50 weapons to survivors, depending on the chance you have to find a weapon that round). The sooner you get to the Barret, the better.

Noted.

You've been playing this for more than an hour, I take it.

Always shoot for the head and try to be directly in line with the target.

Yep surviors first and keep the chainsaw as your secondary.

Lasted six days, but didn't realize until the end that the game detected headshots.

The second time I made it through all twenty days. Once you get six survivors and automatic weapons, it's pretty much trivial to win (though fun). A refreshing change from the usual Resident Evil 4 strategy (in RE4 the shotgun and rifle are the best weapons, and automatics are worthless--here it's the reverse).