FBI agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) have been reassigned from their usual job of investigating the X-Files (unexplained FBI cases involving the paranormal) to investigate a bomb threat against a federal building in Dallas. At the same time, a young boy in Texas discovers a cave with the skeleton of a Paleo-Indian who'd died in combat with an extraterrestrial...and the aliens' nefarious mind-controlling black oil. It turns out the bomb threat and the cave's contents are related, and our favorite FBI agents find themselves once more locking horns with the nefarious Syndicate and mastermind The Cigarette-Smoking Man...
*The opening scene where a pair of Paleo-Indians hunt down an extraterrestrial in Ice Age Texas was awesome when I saw it nearly twenty years ago and it was still a lot of fun. As Nick pointed out, this was before CGI became so all-encompassing. That's a real alien there, not a video-game creation. And the cave-men display some tactical sense--they're fighting an enemy with gigantic eyes in the dark, so they use their torches to disorient and blind it.
*There are some really good character moments. One of the most entertaining moments is Scully (a medical doctor) diagnosing her own symptoms as she goes into anaphylactic shock after getting stung by a bee. When we first see Mulder and Scully, their bantering shows a lot of what we need to know about them as people. We don't need to be told much if anything. And Mulder makes a great speech to Scully at one point.
*Per the above, the film was designed to appeal to those who weren't already X-Files fans. Mulder's back-story comes out in a drunken rant in a bar, for example.
*We learn some interesting stuff about the aliens and the Syndicate. I won't give away a lot of information for spoilery reasons, but there is a quote from The Two Towers by J.R.R. Tolkien I found appropriate: "It is difficult with these evil folk to know when they are in league, and when they are cheating one another."
*The movie is very 1990s. There are references to the Waco siege and the Ruby Ridge shootings. The Dallas bomb-threat is very reminiscent of the 1995 Oklahoma City Bombing in terms of both concept and visuals. I remember reading somewhere that the government conspiracies, aliens, etc. were what filled the gap between the end of the Cold War and the beginning of the War on Terror and that's plain here. There're even references to the dangerous African "killer bees" and the all-powerful Federal Emergency Management Agency (here're some comments on FEMA from a conspiracist POV) that are very 1990s. Heck, the movie even has a character refer to FEMA as "the secret government."
*There's a really good cliffhanger "WHAM!" moment I did not see coming. Bravo.
*If the aliens that the Syndicate is working with are that old and powerful, why the need for the conspiracy in the first place? The British were only a few thousand years' more advanced in terms of technology and organization than the Stone Age aborigines of Australia and they didn't need indigenous proxies to work for decades to prepare the way for them. They just swept in, took the lands they wanted, and wiped out most of the natives in the process. To cite the Dalek from Dr. Who, a conflict between them and us would not be war, but pest control. There's an in-universe explanation involving the leverage the early Syndicate had, but given the back-story revealed for the aliens, I don't think that would work.
*To that end, it would have been better if the prologue took place in the 19th Century or early 20th Century, using Comanche Indians or cowboys instead of cave-men. This would show the alien colonization scheme was only a few decades or a century old. The aliens would be a powerful and dangerous opponent, but weak enough that they couldn't just sweep right in and take over.
*Mulder manages to get to Antarctica at one point in 48 hours. That seems to be pushing it, especially given how he's likely being watched. It would have been better if the events in Antarctica took place in, say, Canada. It would be closer to the Syndicate's North American center of power and wouldn't take as long to get there. Mulder wouldn't need to buy plane tickets or anything else that could give away his location--just drive there.
*When a Syndicate base is collapsing, one of the minions asks about Mulder. Why do they even care about him? He's their enemy and the only reason he isn't dead is because he has allies with leverage on the Syndicate (I think in one episode Assistant FBI Director Walter Skinner tells The Cigarette-Smoking Man that if anything happens to Mulder, some damaging information is getting released) or because they don't want to make him a martyr ("kill Mulder and we take the risk of turning one man's quest into a crusade"). Him getting killed in a way that doesn't look like a murder would be good for their plans.
*A character is shot in the head at one point (but not lethally). We only see the wound intermittently.
*There's a scene that I described as "the alien water-slide of doom" that should break a character's legs (or at least hurt him rather badly), but it really doesn't.
It's an entertaining film that you should go see, especially since they're reviving the series. 8.5 out of 10.