The question is, "is the X-Files fit for the big screen?" There are, obviously two ways to answer that, yes or no. But the real answer is both.
The concept of the X-Files tv show is perfect fodder for the big screen, including fleshed out, driven characters, epic storylines, and plenty of opportunity for special effects and cool sets. If you've never seen the television show, the movie does a competent job of separating the movie from ongoing storyline for new viewers, while subtly incorporating X-Files mythology for all the X-philes out there.
The basic result is, however, only a longer bigger budgeted episode of the series. While much was brought up, not much was resolved, which led me to thing that it was a 2 hour plug for the 6th season for which you had to plunk your $7 down for. Starting off with prehistoric "cavemen" trudging through the white of the snow covered Texas terrain, the cavemen attack, and are attacked, by a trio of shadowy (for effects purposes) aliens. The last living caveman, standing over his extraterrestrial victim is soon covered by a black liquid streaming from the alien. Flash forward to Texas, 1998, and 4 boys encounter a caved in section of land. One falls in and is soon covered by a similar black ooze. Not long after that, unmarked helicopters, big tanker trucks, and dozens of military and envirement-suited men arrive on the scene, they're motive's obviously not kosher.
We meet Dana Scully (Gillian Anderson) and Fox Mulder (David Duchovney), working routine FBI bomb hunt duty, since the X-Files (as we are told) has been closed down (yet again). Proceed to the building blowing up, reminding you of the lead-in scene from Lethal Weapon 3 (only this building explosion serves a purpose). FBI investigation into the bombing concludes that Mulder and Scully should be separated from working together, and Scully agrees as she begins to doubt her role as yin to Mulder's yang.
But Mulder meets a kooky conspiracy theorist/informant (Martin Landau) who leads him onto the trail he's been seeking all his life, proof of extraterrestrial existence, government knowledge of their existence, conspiracy to cover their existence up, and a global conspiracy of powerful people working with the aliens.
But it turns out the men who had thought they were working with the aliens are actually being duped and manipulated by them, as the aliens are not just trying to merge with humanity, but trying to replace them (through a system similar to "Aliens" where the e.b.e. gestates inside the human, feeding on the innards, then eventually emerging).
Typical of the X-Files, the powerful men see Mulder getting close to the truth, and they try to stop him by kidnapping Scully, and giving her to the Aliens. One of the men, regretting his affiliation with the secret group, gives Mulder the key to saving his partner, and so Mulder ventures up to the Arctic to find the alien breeding ground.
And in typical fashion, Mulder saves Scully, sees the ufo which Scully didn't, testifies to a disbelieving committee about his actions, and the X-Files are reopened by a mysterious power... the end.
As I said, the movie is a 2 hour regular episode, it follows standard X-Files format virtually the enire time (the only deviation is the overt exposure of the aliens), which is a disappointment upon itself (I was expecting more... silly me). It's good because it does explain things a bit more to the avid X-phile, like what the black cancer is, the motivations of the secret council, and, perhaps, even letting Scully believe Mulder for once. As I said before, the big conspiracy is also narrowed down well so that the infrequent X-Files viewer can understand what's going on.
It's a must watch for the X-Files fan, even if you don't like the end result (like the almost-kiss between the leads) and it's probably a better movie for the uninitiated X-File viewer.