Science fiction and action are two genres that seem to combine naturally. Most sci-fi writers love depicting how aliens or humans of the future might one day wage war and action is the ideal home for that content. Their collaboration is not only common but it's also resulted in some of the best examples of both.
The quintessential 90s sci-fi action movie is probably Terminator 2: Judgement Day, but, while that film is a classic, there are already infinite detailed descriptions of its greatness. Not every fun futuristic shoot-em-up gets to spawn a billion-dollar franchise, some have to make do with middling sales and the occasional fond look back.
The Rocketeer
So many classics of the 70s, 80s and even the 90s were built from the DNA of the early film serials that inspired them. Everyone knows the obvious ones like Star Wars and Indiana Jones, but those early works still hold influence everywhere from westerns to crime fiction. The Rocketeer sought to create a direct homage to those classics and landed on a solid superhero romp in the process. The film struggled in development hell due to conflicts between the creatives and Michael Eisner, and its eventual release was a mild financial disappointment. This is tragic because the lovingly anachronistic tale of Cliff Secord's incredible rocket pack and the corrupt goons who seek to steal it from him is an absolute joy. The performances are solid, including Paul Sorvino and Timothy Dalton in fun villain roles and Billy Campbell as an excellent leading man. The Rocketeer is outdated on purpose and in a good way, and it deserves a closer look, especially as retrofuturism comes back in style.
Guyver: Dark Hero
To sell Steve Wang's 1994 adaptation of Yoshiki Takaya's ongoing manga series in a single sentence; it's R-rated biopunk Power Rangers starring the voice actor behind Solid Snake. Dark Hero is actually the second adaptation, as it came on the heels of the poorly-received 1991 film. The title is quite literal, as the sequel aimed to create a film much more in line with the source material's gritty themes and visceral violence. David Hayter stars as Sean Barker, a young man who has bonded with a symbiotic alien to become The Guyver. Barker must travel to an archeological site to discover the grim past of his alien partner while tangling with fellow alien-enhanced warriors and attempting to destroy the company that gave him his power. Guyver: Dark Hero is a brutal action movie, occasionally moving into horror territory, but it is a stellar escalation of the ongoing Sentai craze that more fans should check out.
Timecop
With a name that silly and Jean-Claude Van Damme in the starring role, fans of classic action schlock know what they're in for. Of JCVD's expansive action catalog, this 1994 adaptation of a Dark Horse comic is possibly the best. Van Damme portrays Max Walker, a federal agent who joins the nascent Time Enforcement Commission to prevent any abuse of time travel. Walker finds himself hopping through time, trying to stop the illicit schemes of a corrupt politician. The plot doesn't make a ton of sense, often running into many of the classic time travel issues, but the action and emotional catharsis still work. Van Damme never made anything approaching high art, but Timecop is a unique and interesting action piece that justifies its existence through sheer spectacle.
Virtuosity
This bizarre lurid action film uses a series of insane high-minded sci-fi concepts to put together a deeply weird experience. Denzel Washington stars as Parker Barnes a former cop, stuck serving a nasty prison sentence after killing the terrorist who slew his family. Russell Crowe stars as SID 6.7, an AI comprised of the living consciousness of every known serial murderer in human history and one of the wildest characters ever put to the screen. SID makes it into the real world, leaving Barnes to race against time to save a small army of hostages from SID's wrath. There's a lot wrong with Virtuosity, but it's the kind of oddball 90s pitch that would never get off the ground in the modern era.
Demolition Man
Sylvester Stallone has seemingly appeared in just about every kind of film it is possible to imagine one starring in. His sci-fi offerings vary in quality, as does the rest of his output, but this 1993 entry is easily one of his best. Stallone appears opposite Wesley Snipes, the former is a renegade cop while the latter is a flamboyant terrorist. Both are imprisoned and sentenced to cryogenic freezing. They awaken 36 years later in a world dominated by an oppressive nanny state that has successfully resolved all human violence at the cost of freedom. Society hasn't seen crime in ages, so Snipes' anarchic antics put the world into chaos, leaving Stallone's mastery of violence to save the day. Demolition Man is a hilarious blend of 90s action spectacle and comedic social commentary that rings true to this day.