F - In all honesty, there was simply just about nothing I enjoyed about this show. Let me preface by saying that I haven't actually seen S4 (except for bits and pieces and the finale). But to me, the problems I have with everything prior to that mean it doesn't actually matter. I will comment on this point at the end of this text.
IMHO it did nothing with its premise, instead dwelling mainly on stories and themes that would have been better suited to the 24th century (or later) setting. Making matters worse, I felt that most of the episodes were really poorly written and unengaging.
I think the biggest complaint I have about the show (although the top one already is pretty major, I guess) is that none of the characters did a thing for me. I felt they were a bunch of bland, directionless and - if you will - faceless people who ended up meaning nothing to me. And that, in the end, I think is what really defines whether you become invested in a show or not.
One of the prime examples is Archer. I love Bakula as an actor. But here, I thought the character never once really felt like a Captain. He just didn't exert the necessary sense of authority and dignity. He just seemed like a guy who happened to be the Captain, and his crew listened to him mainly because the show was written that way.
However, the problems I have with the show don't end there. One thing that bothered me a lot was the design of the Enterprise (outside, but mainly inside) as well as things like costume design. If you're doing a prequel, you simply have to do certain things to support the feeling that it's a prequel.
I felt there was nothing about the designs that even tried to do that. As far as I can see, they were going for a very utilitarian design. But IMHO that doesn't work within the context.
If you look at the new Star Trek film (I have to base these statements on screenshots and trailers since I haven't seen it myself), it's very stylized. It uses 50's- and 60's- (maybe even some 40's-) -inspired designs that allow it to look modern yet feel retro at the same time. That way, you're able to create a modern film that still actually feels like a prequel. And that's exactly what I felt ENT should have done. I don't know they didn't do it, mind you.
Before I finish, I will say that I probably would have given season 3 on its own a D. I really felt it was "weak but enjoyable". That sums it up very well for me, mind you. However, if I look at the show as a whole, I simply don't feel a D is suitable.
I mentioned up above that I haven't seen S4 and that that wouldn't change the grade I picked. The reason for this is that - for me - the characters had been basically destroyed within seasons 1 and 2. I just never felt I could take them seriously form that point onwards. So it doesn't really make a difference how 'good' S4 might be. It's using characters that don't work for me. And as I said, the characters are really at the core of it all. If they don't work, nothing really will.
And, really, the only reason I even watched S3 was that I was longing for some Trek nostalgia from new material. It had just about nothing to do with me actually wanting to see ENT or its characters.
I'm happy for people who enjoy the show. I just don't see anything enjoyable in it myself.