I thought it was a pretty good movie, though not the best ever; it had its highs and lows, although possibly I'm the only person who saw it whose enjoyment was impeded by the fact that I was wondering 'What the hell happened to mutate that retrovirus?!?' sweatdrop
For myself, though, the thing that really helped me enjoy the movie was thinking about what would happen were I in a similar situation. Deer-hunting and zombie/vampires aside, the sheer isolation would definitely get to me, one way or another; the part when he's talking to the mannequins was bizarrely poignant, which - along with the dog dying - was akin to Wilson drifting off in Cast Away.
One thing that bugged me, though: The end, where he gives the vial of blood to the woman et al, confused me. Didn't he manage to create it through being an awesome bio-something-chemist? What are the odds that another survivor - given the apparent pandemic nature of the disease - would have the skills necessary to replicate an antidote? Shouldn't Neville have thrown the grenade and gotten in the safe too?
(Spoilers just in case anyone still hasn't seen it.)