I put forth the Mortal Kombat movie that never quite made it as an excellent example of cinematic creativity straying from the original idea. Can you seriously say this would not have been fucking awesome as a full length?
I guess if you're really into something and they finally release a movie, and its not true to the franchise, that's super disappointing. But you shouldn't declare it a terrible movie, just declare it a terrible representation.
But the thing is, when it comes to some* franchises (such as the aforementioned Star Trek, where its strength is in its fifty years continuity ever-so-skillfully weaved together), a terrible representation IS a terrible movie. It shows sloppy writing, and a total disregard for the established storyline of the entire universe in question.
I mean, yeah, Star Trek 2009 may be an entertaining bit of action, but being entertaining alone does not a good movie make, especially when it is hacked together so sloppily. When it comes to some franchises, continuity is literally sacrosanct.
I enjoyed that Mortal Kombat clip, but in all honesty, I'm not big enough on the franchise to actually care about whether or not it's canon. I'm sure if I was super into it I would probably have a more in-depth opinion.
*Note I said some. Not all.