Youtube has sections of it but not the entire film. These are in a playlist, which should autoplay from here:
There are significant gaps between each section, but it gives a good idea of the style and level of violence and gore. The available segments are linked at youtube.
Roger Ebert gives it 4 stars and says, ""Dawn of the Dead" is one of the best horror films ever made -- and, as an inescapable result, one of the most horrifying." 1000 Misspent Hours praises it but finds fault with the zombies: "Because it’s next to impossible to fear something and pity it at the same time, these zombies can’t pack the same punch as the ones in Night of the Living Dead." Moria says,
Dawn of the Dead is about questioning the values that the survivors are trying to fight for. And as such Romero has construed Dawn of the Dead as a remarkable metaphor for the numbing effects of materialism and the complacency of consumer society.
Slant Magazine closes with this:
As countless undergrad thesis papers have already delved into in far greater detail, the cumulative effect of these thematic reversals points to Romero's big message: that if the often bleak '60s of Night were defined by their radical political activism, then the insipidly optimistic '70s of Dawn are a testament to the politics of retrenchment, consumerist balm and self-immobilization..... but Dawn's most unsettling aspect is in how it shows us how little we've changed as a culture.
The New York Times reviewer left after 15 minutes, because he has a problem with zombies: "I have a pet peeve about flesh-eating zombies who never stop snacking. Accordingly, I was able to sit through only the first fifteen minutes..." Sheesh. Variety pans it.