Now that I'm not the first, I'll toss my answer into the ring.
I think Prometheus is a VERY good film. I also think it's very close in style and feel to the original. Is it the same? No. The audience of today is different from the audience of 1979. Today, if you want a film to be a commercial success, you have to meet a certain level of activity and visual appeal. If you have more than about 10 minutes without an adrenaline s[pike, audiences will say the movie was "slow" (yes, a bit of sarcasm here, but just a bit). I also think the rest of the Alien series has a much higher level of action vs. suspense, which colors some peoples memories.
I'm going to give a very high level outline of Alien, which I watched the Friday before the Prometheus opening, just to refresh my memory and recapture the feel.
The film opens with a ship is in deep space on a mission that requires sleep capsules during the travel. The computer wakes the crew to investigate an anomaly. The crew finds a planet with a harsh environment requiring suits to breath. Signs of industrial manufacture are found. A room of containers is located. The containers hold a mysterious living thing. Someone becomes infected. A living creature gestates within a member of the crew. The creature gets out and grows larger in a very short time. The crew begins dying off through a series of events, all violent. At the end you have a female member of the crew leave the original ship in a "lifeboat" with a non-human. They are the only survivors.
Now, I could do the same thing for the Prometheus film. But you'd get annoyed reading the same text twice. It's the same plot. There are significant differences, this isn't just a cheap remake. Alien has the planet as an unexpected anomaly, while Prometheus has the planet as the intended destination. The infection is through a "face-hugger" in one movie, and through a microbial infection that altered the DNA of someone in the new film. And the list of differences goes on. It is a new film. It is much faster paced and less exposition based. But the big major plot points are the same, or at least close enough to see the the master plot outline similarities.
So, thoughts, comments, rebuttals?