Pretty good
i think anyone who is a fan of the series or has watch a few episodes and felt interested will appreciate this movie. its true that it feels like a long episode, but it stays true to the show's premise, and reminded me of what a great show it was.
the chemistry between mulder and skully is still there, and their characters have grown in ways, and remained the same in ways, as would be expected after several years. this is the most important imo as a fan.
although i feel the movie has done enough to be considered an overall good movie, i'm not sure how it entices people who aren't so familiar with the show. if you're not a fan, think of it on the same level as every other sci-fi thriller that has come out over the last 3-4 years, it's not any better or worse than those.