"Sluggish" is certainly the best word to describe this. In the second half, this is a compliment, as all manner of slimy, tenticular or wormy ickiness gets hurled in your face with gleeful abandon. Unfortunately, it follows on the heels of a first half that takes far too long to get going: part of the joy of good 80's B-movies was their absolute refusal to waste time on characters who were going to die anyway. Writer-director Gunn attempts to make us care, with a lengthy set-up which establishes far more than necessary. Meteorite. Hicksville. Someone gets infected. Worms and zombies attack. There, that's all you need, in seven words. Other stuff, such as the sexual tension between the hero and heroine is superfluous, redundant, and frankly, gets a little irritating.
But once it stops faffing around, and the slithering promised by the title actually starts, it becomes much more entertaining. Rooker makes an impression as Grant Grant [sic], the creep round whom the invasion centers; his mannerisms convinced me that being slug-possession would be a step up the evolutionary scale for his character. I can, however, see why it tanked at the cinema: why bother spending $9 to see a film, whose main influences you can rent for a week and pay about $1.99? [Nods include The Thing, Videodrome, Tremors and Basket Case, but as Applseed kindly reminded me, Night of the Creeps is likely the biggest influence] The FX are generally good, if occasionally a bit too CGI-ish; however, Gunn's origins with Troma are readily apparent in some eye-popping gore. It all builds towards a messy finale, like Society meets From Beyond, in which exactly everyone dies whom you'd expect. While you might as well hang on until it hits video - or better yet, cable - when it does, the second half, at least, merits some attention.