The one true problem with Archer, is the writing. Far too often he is written in an overly simplistic way. He doesn't seem 'new' to space as was intended....he seems new to command, strategy and basic diplomacy.
This. A huge problem of ENT was that they wanted to trade on humanity's naivete and Sensawunda at this point in Trek "history"... but had no clear idea of how to do that or what the lines should be. I think this ultimately is why ENT's human characters feel much more tepid and uninteresting than they needed to feel (it's not just a problem with Archer, there was a tentativeness and confusion in writing all of them).
Take, for example, my personal #1 worst episode in the franchise, A Night in Sickbay. This trainwreck of an episode is 45mins of character assassination. Archer is depicted as an unstable, unreliable, irrational idiot. It severely damages the character in my eyes.
Yep. And ENT was plagued by a lot of that (although "A Night in Sickbay" was probably the most extreme example).
There were a lot of nice ideas behind ENT, as there were initially behind VOY. Unfortunately it's the execution that really makes or breaks a show. Some believe that great actors can rise above badly-written material; I don't think that's as easy to do as is popularly imagined. It's far easier for bad writing and conception to drag down what would otherwise be fine performances.
(Same goes for some of the Janeway criticism, I think. Yes, some of it is just sexism, and yes, obviously the character is conceived to be a competent manager put in an impossible corner and forced to Make the Tough Decisions. But if the writing doesn't really sell the circumstances or the decisions, there's only so much the actors can do.)