I was once asked on Reddit how I would have done Enterprise, I think the response is appropriatte to post here.
The problems, for me, arose with the season finale of Season two, with the Xindi storyline. I was actually interested in the Temporal cold war, and thought that, if they had continued the episodic nature of the show, holding off on creating new canon, and explaining inconsistencies in the old. For example, it was established in TOS that Earth and the Romulans fought a war using Nuclear Warheads and communicating by radio.
Why? Why was it just Earth? Why didn't Vulcan assist? Why were Nuclear Weapons used? Why was communication restricted to Subspace Radio?
The creators of Enterprise decided to ignore the canon, rather than explain it.
To me, they could have explained everything by merging the Romulan War and Temporal Cold War plots. Have the Romulans operating under the direction of agents (not direct knowing cooperation) from a future iteration of the Romulan Star Empire.
Weakened by the Dominion War, shattered by an internal strife bordering on Civil War (between the Imperial and the Reunification factions), the Tal Shiar sends three agents through time (via Solar Slingshot time-Warp) to improve Romulan fortunes in the past to rewrite their present.
Two go back to the mid 2100s, to provoke and, hopefully, eliminate the burgeoning Federation. Specifically, by eliminating their most influential member, Earth.
Valdore, a future Romulan, infiltrates the Military, and with his advanced future technological knowledge, as well as a personal datapad chock-full of the weakness', policies, and tactics of period enemies of the RSE, he advances quickly through the ranks, heading up the projects that would give rise to Quantum Singularities as power sources and Plasma-Torpedoes, though he discovers that it was overlooked that a necessary material resource would be unattainable by Romulans until the next century.
Another future Romulan, Drax, infiltrates the Romulan civilian Government. By using historical files detailing the personal failings and family details of period Romulans, he takes control from behind the scenes of the Council.
Together, Drax and Valdore conspire to manipulate Romulus into the Earth-Romulan war far sooner than history intended, hoping to catch Earth alone and unaided, before the Federation can be founded.
The third agent was supposed to be sent to Earth, sometime before Zephram Cochranes warp flight, in order to sabotage the missile he would have used, in such a way that it would explode before Cochrane got to Warp, however, his slingshot calculations were off, and he ended up, not in orbit of earth during WWIII, but in orbit of the Suliban homeworld, 50 years into his future. He's shortly shocked to discover, only a few months after he left, that a disaster annihilated the Romulan Empire (this would be left unexplained and vague, for future developments in the prime storyline, and leaves it open for the ST:XI to remain canon).
So, rather than giving up, he approaches the Suliban. Promising them a ripe, better future, he arranges for them to cooperate with him to build a Temporal Communicator, to guide and manipulate the 22nd century Suliban, as he believes the other two agents were similarly mis-targeted.
This is the first conflict in the Temporal Cold War. Daniels is trying to aid and prepare Starfleet for the conflict by guiding events in such a way that the crucial encounters and liaisons are formed earlier than expected and quickly, that's why he manipulated events to lead Archer to P'Jem, to encounter Shran. That's why he arranged, through third parties, the escape of the Augments and the Klingon Augment Virus Incident that let Archer deal with General Krell, which allowed him an "in" with the Empire at a later date.
During one of the first battles of the Earth-Romulan War, the Columbia is lost after they're forced in battle to scram their Warp reactor, but the crew manages to escape in her escape Pods and Shuttlepods. All but Captain Benteen survive, who rams Columbia into the Romulans shields. The resultant explosion of the Columbias Impulse Engines (fusion powered) reveals to the survivors the Romulan shields weakness against Beta Radiation.
All of this would lead to the Warp 7 project, and the design of the Daedalus class Explorer, which would serve as the mainline ships during the Earth Romulan War alongside the (now obsolete) NX Class vessels Enterprise, Challenger, Discovery, Atlantis, and Endeavor.
Boom, canon preserved, canon explained, and we avoid all that silly Xindi business.
I liked Enterprise for the ideas it brought, seeing early Starfleet technology in action was an interesting concept. No shields, no tractor beam, unstable transporter technology. It was nice.
As a captain, Archer was very arrogant, but he's nowhere near the Janeway standard of douchebaggery. Yes he made some dumb decisions, but at the end of the day, he was trying to prove to the Vulcans that the Human species has improved over the years.
Now, where the show failed, like others have pointed out, was that the plot for 80% of the episodes didn't feel like Trek.
I, for one, dislike the whole Xindi and Temporal Cold War concept, because it dragged on for way, way, way too long (an entire season if I'm not mistaking).
The main villains, were trans-dimensional beings, who could have been easily stopped by the Q (the guardians of the universe, yeah right), but nope. Let's send the very first Human star cruiser, with ancient technology, to fight against an armada of advanced warships.
The 29th (?) century Fed did very little to actually help Enterprise.
"Hey, we know that the fate of our entire past is in your hands, but we can't send a few ships back in time (they have the technology), because of the whole :we can't change the past to save our asses: prime directive.
What could they have done instead?
Hey, remember the Vulcan-Andorian war? How about we put more emphasis on that?
Hey, remember the "explore strange, new worlds" part? Since this is the very first star cruiser, how about we put more emphasis on that?
Enterprise could have been successful, because it has the basic ideas, but the final product gave you this feeling that the writers tried too much to come up with something different.
Like it wasn't enough of a difference to see the early Fed technology in action, or the founding of the Federation.