Just finished SH3.. first time through on normal/normal was just under 6 hours (and the last hour of that was the end boss, I had 10 bullets and no health when I fought him GRRRRRRRRRRRR).
Overall, I have mixed feelings. The graphics/sound/production were absolutely top notch, but the gameplay was 'eh'. The first 2 hours (1/3rd of the game) were absolutely useless with no plot information(mall, subway, office building), and don't even fit into the context of the game at all. The story was just... something else. I'm going to have to hunt down a used copy of SH1, because I didn't understand a single damn thing.
IMO, the graphics/sound/production values of SH3 are incredible, but SH2 is still the better game overall.
I'd say..
Graphics: 9.5/10 (I want to give it 10/10, but that flashlight...)
Sound: 10/10 (Truly amazing, and they cut down on the irritating static from SH2!)
Gameplay: 5/10 (Go here, go there, go somewhere else, flip to Dark World, rinse and repeat)
Story: N/A (Going to refrain from scoring it here, as I haven't played SH1, and thus didn't understand anything, at all, but that alone should tell you something)
Overall: 8/10 (Production values alone make this a great, if 5 hour long, experience. Think of it as an interactive, double length horror movie)