Let me start by talking about the good things!
- Captain Archer. Scott B. does a fantastic job, playing the main character of the series. He pretty much carries the entire show, and if not for him, I think it would have been cancelled even sooner. He's right up there with Patrick Stewart, in terms of acting range and talent. I only wish they had cast him in a different Star Trek series!
- Commander Tucker. "Trip" is the chief engineer, and he's a pretty good character, for the most part.
- Doctor Phlox. The third character who's pretty good. He's an alien, and he's a friendly person. It takes a while to get used to his mannerisms, and the "he has exotic pets" joke wears thin quickly, but he's okay.
- Shram. Shrem? I don't know how to spell it. Anyway, he's an Andorian who serves as a minor antagonist. He was so good and interesting, that they kept bringing him back for more episodes. This continued to the point where they decided to make him a main cast member...but then the series got cancelled. Darn. He could have been like Seven of Nine on Voyager, who joined the main cast in Season Five and made the show incredibly awesome.
- Special Effects. The series has great special effects, probably because it was made after the year 2000, unlike the others.
The second main character is T'Pol, a female Vulcan. She was clearly hired not for her acting ability, but for her large chest and willingness to do nude scenes. The very first episode has a gratuitous scene of her getting rubbed with lotion, and it was awful. It pretty much sets the tone for her character, for the rest of the series. Her acting got better as the show went on, and they tried different things to make her character better, but the show never really got past the fact that the second main character is eye candy. She was awkwardly shipped with all the other male characters, until they settled on a badly-done on-again, off-again relationship with Tucker.
The show is a prequel series, meaning it takes place before the first Star Trek show. There were several episodes, where the premise was "Earthlings meet [thing from a different series] for the first time". Those episodes tended to be bad and somewhat derivative. Another common storyline was "technology problems which only exist because the show is set in a low-tech era". It's sort of like if, today, they made a show about the 1980's where all the problems could easily be solved with a smartphone. My wife hated those episodes. And the third major storyline which was considered a failure is the "temporal cold war" storyline, where people from 600 years in the future came back to this time, so they could fight each other by proxy. I thought it was a neat idea, although it didn't play out in the best way.