Star Trek Enterprise has had some outstanding episodes this past season. Unfortunately, the level of quality became so dismal in the prior two seasons (two and three) that most of the fans completely gave up on the series. (I don't know a single person who still watches it.) Head writer Manny Coto was brought in at the beginning of the current season and has, in my opinion, completely redeemed it. Not only is the writing far superior to nearly everything that came before, but we're finally getting stories that tie in closely with the original series (the one with Kirk and Spock).
The most recently aired storyline, entitled "In a Mirror, Darkly", was a two-parter that took place entirely in the evil mirror universe (the one where Spock had a beard). The opening credits were altered to show scenes from the history of the Empire (rather than the Federation), and the music was replaced with evil music. The story was based around The Tholian Web from the old series, and we get a lot of new information. It seems that the reason the Defiant was fading out of our universe was that the Tholians in the evil universe had created and inter-dimensional gateway from their side and lured it in. In other words, it was fading out of the good universe and appearing in the evil one 100 years earlier. The evil Enterprise crew steal it from the Tholians and use it as a war machine. Not only do we get a good look at the interior of a Constitution Class starship, but we finally get to see a Tholian up close. Oh, and there's also a Gorn. (I don't actually know why there's a Gorn, as it didn't seem to have anything important to do with the story.)
So Enterprise ultimately proved to be salvagable but not savable. It has been cancelled, and there are only three new episodes left. If this weren't the case, I'd recommend you tune in. At this point, though, you should probably just wait for the Season Four DVDs coming out later this year.