The people at Star Trek: New Voyages liked Original Series Trek so much that they decided to continue the original five-year mission. Only with different actors, of course.
You might think this is just another fan film project, but this goes beyond the usual fan films. They're working with Gene Roddenberry's son, and they appear to have some sort of approval from Paramount, though I'm unclear on the details. They've made two episodes so far; you can download them from the site, either as one huge DVD file or in eight-minute segments.
They've lovingly and skillfully recreated every set from TOS, and the costumes, and even the lighting and sound effects. The production design is pretty near flawless. The theme music is different—I'm guessing they couldn't get the rights. The special effects have been updated a little, but still fit in fine with the decor. (The site says they're trying to make "a Trek that looks as modern and flows as fast as any action adventure show on TV today," but to me it looks and feels more like the original. Though I've only seen the first eight-minute clip so far, so I may not have gotten the full effect.)
The only things that seem a little off to me are the acting and the writing. If you think of this as an amateur fan production, the acting and writing are fine; if you think of it as a professional production (and it's easy to fall into that, 'cause the look is so well done) then it's a little disappointing, at least to me. Of course, I haven't watched any OS episodes in quite a while, so I may be giving the original acting and writing too much credit. But what I've seen so far of the New Voyages felt a little sloppy.
Still, definitely worth taking a look, if for no other reason than the mildly surreal feeling of watching these other actors play the characters. I think the casting's a little odd—in particular, Kirk and McCoy look too young to me, compared to Original Series photos—though as Karen pointed out to me, these days on TV looking HOTT may outweigh any trivial concerns about plausibility of age.
Anyway, don't take my word for it; go take a look.
(Thanks, Jeff K!)