ENT was too safe. They took very few chances with character creation and development, plots, etc. It didn't have the right feel of the first deep space explorers, more like TNG in a smaller ship (the exterior of NX-Class is pretty awful IMO, though the sets were pretty good).
The first two seasons were, on the whole, pretty weak. Things started to pick up with S3, where they did take a couple of risks and didn't do a VOY and rely on Janeway's reset button.
As for the characters:
- Archer bugs the hell out of me, he comes across as incompetent a lot of the time, whilst his Vulcan racism was just so forced it was cringy to watch
- T'Pol I'm really pretty ambivilant towards, she was alright, nothing stellar, but her Vulcan pout got bothersome after a while (one thing that does tick me off is why she wasn't in a proper uniform in S4)
- Tucker I liked, and not just because he's hot (major plus though), but he was definately very human and the loss of his sister gave him a nice little arc
- Reed is little more than a stereotypical stiffer-upper-lipped Englishman, which gets tired very quickly (why they never showed him and Hayes getting it on still baffles me--just look at the sexual tension!!!!)
- Sato was another alright character, the academic rookie, but she did have some growth, though her amnesia was pretty bad in S1 (in "Broken Bow" she doesn't seem to have a weapon even though she is rated with one, and when grabbed by Klingons just screams like a little girl although is loater revealed to be a martial artist)
- Mayweather was pointless, little more than an extra with a name (he was some eye candy though)
- Phlox was alright as well, with his interesting way to treat injuries and illnesses he can definately be called unique, though I could've done without knowing he's a nudist!
The way ENT should have gone should have been to "pick up" where DS9 left off (not literally of course). Set the series in 2161, just after the Romulan War, so they had to deal with all the hard work and problems caused by such a massive conflict, as well as the newly formed Federation with various aliens. Have the ship be the first collective assignment, so you have member races all working together on the same ship for the first time and just watch the sparks fly. There would be lots of potential for character conflict as well as some alien viewpoints, as they try and figure out the best way to live and work together. That way we could have had Shran from the very beginning!