Enterprise was a great show, and it was cancelled just when it was coming into it's own.
For me the Xindi season was a bit of a let down; although audacious in scope, the extradimensional alien race macguffin was a bit of a dud and Xindi Reptiles themselves were black-hat villains with no character, a foil for the reversal of the the Xindi toward Archer's POV. Instead of timeline-muddling aliens they could have had a less-advanced species with the same earth-based fears as a front for Romulan interests, the first advanced echoes of the coming war.
As to the last episode, why not have shown the Battle of Cheron, leading to the creation of the UFP? The holodeck idea was interesting, but as the end of series? No way, a mid-season tribute like "First Flight" perhaps, but trying to out redo "All Good Things..." was lazy - Enterprise had it's own great characters, why rely on old favourites as spectacle? Killing off Trip was just gratuitous, especially as he was one of the best; a throw-away device to create a resonance amongst the viewers akin to the death of Tasha Yar.
But overall, the show had great actors in the leads, more family than Voyager was after seven years, and it's a bloody shame not have seen them develop over time like in DS9.