Mishandling of Canon - I'm not sure what you mean by this, though I'm guessing you meant to say Continuity rather than Canon. While there were some continuity oddities, I'm not sure any of them were particularly more egregious than those brought up in other series.
I voted this, because it was the main reason why I avoided the series up until just this past year.
While they got the technology about par for the time period, the look of the starship made it look like something you'd see in DS9 or Voyager (I'm talking about the exterior, not the interior)
And yes, I'm fully aware that they couldn't try and make the ship look more primitive then what they had on TOS like using rocks and sticks to move the ship through space, but that's beside the point... the blue warp nacelle in my personal view were way out of place considering they never had those until TNG and the Phoenix in First Contact matched very closely to something acceptable for being prior to TOS.
^ There was nothing fancy or glowing and it not only matched closer to how today's technology looks, but it doesn't exactly over shoot TOS's looks either.
They could have smoothed out the plating on the hull just a bit and made the color of the hull a little bit closer to a white like the TOS starships..... it would have been just fine for today's viewers.
Mind you, I'm also an artist/3D modeler/animator/graphic designer, so these type of things urk me when I can think of several different ways they could have designed the exterior to suit a decent balance between something ahead of today's real life technology and before TOS.
(Believe it or not, it is possible to do, despite the continual arguments of 1960's or 50's reference comments..... for those who keep using those counter-arguments, you're missing the point)
I have no issue with the interior of the ship, nor do I have an issue with the level of technology they had at the time...... but you know what they say about first impressions and my first impressions were from shots I saw of the ship before it aired and what I saw in commercials..... in other words, it didn't look like it fit anywhere in the existing saga.
But the biggest issue I had all had to do with there never being a "Starship Enterprise" before Kirk's ship.... there was never any mention of this ship, no reference to this ship, no models of this ship in anybody's office/ready room, no pictures, not a single word of these people, the ship, their journey's, NOTHING until this show just got tossed at us and we're told to just basically accept that this ship always existed.
Now before anybody starts, I already heard the baseless arguments that it wasn't an NCC-1701 starship and because it was an NX-01, that excuses it's non-existence until now..... when just about every other form of ship called "Enterprise" throughout history that was worth mentioning was mentioned (Sailing Ship, The Aircraft Carrier, The NASA Shuttle, the 1701's, etc.)
On would think that for this being the very first Starship to leave Earth and venture out and explore.... someone in the future would have seen it as worthwhile mentioning, even if it was two lines in one single episode in any of the previous seriesez....
.... I also heard the baseless argument that because of Picard and First Contact, they somehow altered the time line to allow this little fudging of yet another Enterprise that originally never existed in any sense of the term..... and if that was the case, then to me that'd be a pretty huge dent in the original time line in that Insurrection and Nemesis would have been drastically altered or at least Picard and crew would have mentioned their future being different..... but everything went along fine apparently and I guess they were meant to do what they did.
Now I'm not trying to trash the crap out of ST:Enterprise or claim it sucks, nor am I trying to dispute the various excuses everyone has made up for themselves to excuse this whole situation.... I like the show.... now..... and I'm still getting through the series which I have yet to finish watching. But these were my reasons for not watching the show up until now.... and to be perfectly honest, some of the above still bugs me today, but I can push it aside and appreciate the show for what it is.
And while I imagine many in here will dispute and argue my above positions as being exaggerated and not good reasons to bash it for not being Cannon, you can fool yourselves all you want, but I am not alone in my position on the above reasons.
All they had to do to avoid these issues was name the damn ship something other then "Enterprise" and pretty much everything else could be easily excused..... they had Voyager and the Defiant..... and nobody cared.... they saw those starships as their own ships with their own stories.... but naming this ship the Enterprise only gave the impression that it was part of a legacy that it never was a part of before.
It's still a worthwhile show and I enjoy most of the episodes so far..... but this has always been the biggest problem for me..... it was like a big sign sticking out of the ground saying
"HEY LOOK AT ME!! I SCREWED THE CONTINUITY UP!!!"
Oh.... and the music in the intro isn't all that great either.
Other then that.... good show.
Added:
Oh and granted the other shows all had their own continuity issues, the above are the biggest, most blatant continuity issues that even people who are no huge fans of the show would notice.
Stories and character continuity conflicts are not as big of a deal as key factors like the ships and their looks which everybody recognizes.... you can grab someone off the street who never say Star Trek before, line up all the ships in order of their time lines and most would ask "What happened here?"
My answer would be "I have no clue"
