Kyle Maclachlan (Blue Velvet) plays an FBI agent, Lloyd Gallagher, who gets teamed up with Tom Beck, a streetwise, grizzled cop (Michael Nouri) to catch a hedonistic killer on a rampage. Maclachlan is spot on in his role. I won't say any more, for fear of spoiling it. If you've seen any science-fiction at all, chances are you'll be in familiar territory with the rest of the plot. It's hard to say how original it was at the time, but it bears some similarities to Invasion of the Body Snatchers.
As a late 80s film, it hasn't dated too badly. The music and technology are definitely from that era but the cop scenes hold up well. The special effects are also surprisingly good. The highlight is the transfer of an alien from one body to another. One of the heads is ropey but the other is very effective and on first viewing doesn't even look like an effect.
The rest of the main cast do a half decent job of playing it straight. Claudia Christian (Babylon 5) gets to shoot some really big guns and show her butt cleavage. William Boyett does a good job of looking like he's on the brink of a major heart attack. This is intentional, it's part of the plot, he hasn't just been eating too many Ginsters. There is also a 'blink and you'll miss it' appearance from Danny Trejo (Machete).
So far so good. The main problem I have with it, is that it's not very exciting, or very gross, or very emotional. In fact, it's all quite flat and low-key. It commits the cardinal sin of promising something earlier in the film that it doesn't deliver on later. If I see a little tentacle burst out of someone, in the finale I want to see loads of bursting tentacles whipping around. The technology was available at the time, the facehugger's tail in Aliens is one example, so it's a real missed opportunity.
It's still worth watching, and you never know, you might be one of the people who rates it more highly.
If you like this you could also try:
Lifeforce, Split Second, Dark Angel, Invasion of the Body Snatchers (any version).