If you were describing the synopses of the 1999 films The Matrix and The Thirteenth Floor to someone who had never heard of either movie, you would find your descriptions would be very much the same. Both movies deal with some of the same philosophical and psychological issues, and they have superficially similar elements in common. Although they are similar in style, the two films end up being very different in substance, and their different methods of execution lead to different outcomes.
The Thirteenth Floor and The Matrix share several themes and stylistic elements. For example, both films explore the implications of the philosophical 'brain in a vat' conundrum[1] - they make viewers ask themselves “How do I know my senses reflect reality and not artificial stimuli to my brain?” In both films the characters find their consciousness to be part of a massive computer simulation. Another example of shared style is that it’s appropriate to categorize both films as “postmodern.” The Thirteenth Floor qualifies as postmodern for the same reasons The Matrix does in Dr. Strathausen's explanation. Its “[quotation] of past aesthetic styles” is overt - the computer simulation the characters have built recreates 1937 Los Angeles (almost) perfectly. Its “questioning the status of the real in the contemporary world” is also apparent - there is a twist when you figure out that Fuller's note about how “the world’s a sham” isn't about the virtual 1937 Los Angeles; it's about the “real” 1999 Los Angeles. The two films share other stylistic elements, including a dying-and-resurrecting protagonist.
The superficial similarity between the two films is lost in the details of execution. The Matrix seems to take itself less seriously than The Thirteenth Floor does[2] - it starts with an exaggerated, almost cheesy fight/ chase sequence. Its explanation of how and why “The Machines” have enslaved humans is absurd - almost anyone can come up with reasons why it couldn't work. These elements let you know that the film is supposed to be entertaining, not “hard” science fiction. Throughout the movie the philosophical explorations and over-the-top fights are weaved together - the movie raises unanswerable (about the nature of reality, e.g.) questions, then moves on. The Thirteenth Floor, however, uses the same philosophical questions to provide the basis for its ongoing mystery - who killed Hannon Fuller, and why do things seem not quite right? At the beginning, you see Douglas Hall discover the blood in his apartment, then later he says he “can't remember” whether he committed the murder. Shortly afterward, you’re introduced to the simulated consciousnesses, and learn that when a “user” is using them, they (the “hosts”) have little memory of what's happened. These clues draw you into the mystery, causing you to wonder if Douglas is the murderer, or if you're being misled.
This difference in method makes The Matrix a success and The Thirteenth Floor much less of a success. For example, The Matrix uses over-the-top religious symbolism the same way it uses over-the-top violence - that Neo is supposed to be seen as a Christ figure is blatant. When Neo dies and is reborn, it's not a subtle reference to scripture; it's a part of the film not taking itself too seriously - its purpose is to increase the pre-climax tension, and it's followed by the final exaggerated fight scene. The silly fairy-tale point at which Trinity brings Neo back to life with a kiss breaks the “sacred” mood, making the overt religious imagery tolerable. The death and rebirth of Douglas in The Thirteenth Floor however, serves a different purpose - it turns the resolution of the ongoing mystery into a trite happy ending. The mystery is solved when Jane reveals that the 1999 Los Angeles is a simulation. Instead of ending, a new venture is taken; Whitney jacks into 1937 only to be killed - thus introducing the “mind-swap” phenomenon for later. Then David jacks into 1999 as Douglas, to be killed himself. The death/rebirth angle doesn't recall religious redemption; it's a device used to make Douglas and Jane end up together. Where The Matrix uses a vague prophecy, the apparent death of the hero, and the hero's re-awakening to control pacing, The Thirteenth Floor seems to use death/rebirth to shoehorn a trite love story into a mystery.
Someone asked me what The Thirteenth Floor was about, and I thought about it for a moment, and answered “Well, it's like the Matrix, but...” - the two films share enough to justify this comparison. After explaining the basic storyline differences, my questioner said “Hmm. I never heard of it.” I decided there's a reason for that - The Matrix was more of a commercial success than The Thirteenth Floor because its over-the-top exploration of its themes is much more effective and entertaining.
Notes: