We watch Danny Boyle's debut because we are told it's fresh, it's smart and scary and funny. And, for the most part, it is. It's only 92 minutes and from the off comes on like an express train. We like it precisely because it is NOT a period adaptation nor one of Ken Loach's patronising middle-class diatribes. It looks American.

Then we watch Shallow Grave again and it begins to dawn that there is something seriously wrong with this adrenalised post-Thatcher yuppies-in-jeopardy flick.

The plot we know: three twentysomething professionals look to rent out a room in their Edinburgh flat. After humiliating a string of aspirants they alight on the enigmatic Hugo (Keith Allen), who promptly ups and dies on them. But before they can do the right thing the threesome unearth a suitcase of cash under the dead man's bed and cross an invisible line: dispose of Hugo and they can keep the dosh themselves.

There is still a lot to be admired here. Boyle, along with writer John Hodge and producer Andrew McDonald, know this is a calling card. Thus from the beginning we get the Sunset Boulevard-esque posthumous voiceover, and the fast-cutting montage of (very funny) interviews that firmly establish the three as anti-heroes. The set design is striking, especially the disorienting, cathedralic flat with its shopping centre-size entrance hall. It tells us that we should take following with a shovelful of salt.

The scenes of the shallow grave itself (Hugo has sprawled naked on a deep-red sheet for days, like something out of Peter Greenaway) are oblique, grisly detail conjured by the sound of saws rasping through bone. Visually and aurally the film remains striking, as does its willingness to dispense with pedantic detail.

The problems are more structural. From the start we anticipate David (Christopher Eccleston) to be our anchor. Hodge clearly thinks the same, thus throws us midway by having him the one to snap first. The problem being, as amusing as we might initially find Alex (Ewan McGregor) and Juliet (Kerry Fox), they soon begin to grate. When the put-upon Cameron punches Alex out at the ball we cannot but cheer. And by the time the thugs fetch up, the treatment metered out seems wholly justified. The playing is fine - they are hamstrung by the script.

And, incidentally, has anyone ever stopped to consider that turning the corpse over to the authorities doesn't actually preclude keeping the cash? In point of fact, the heavies might have been forced to reason that their ill-gotten gains had gone the same way. But then we wouldn't have much of a movie, would we?

Eccleston is a fine actor (witness TV's Our Friends in the North), but he can do nothing with the robotic David. When he starts living in the attic, drilling spy holes, the abrupt shift rings hollow. Likewise Juliet's gravitating towards David at the payoff to shift our sympathies on to the irritating Alex. The bald fact is, by the time of the climatic showdown we wouldn't mind seeing them all dead.

The final 'twist' is a one-shot. On repeated viewing it becomes farcical: would David not have checked the case before leaving? And given all that's happened, why does Juliet wait until she's in the car? Alex is clearly going nowhere. It makes for a nice shot but precious little sense, and (with Andy Williams' ironic croon on the soundtrack) points up the huge debt this film owes the Coen brothers. Didn't we see this done first and better in Blood Simple?

All of which is not to deny the film its sense of fun. It's a black comedy that manages to be frequently black and occasionally very comic. It proves that Hodge can write (the incidentals are excellent), and that Boyle is prepared to shrug-off the television straight-jacket so afflicting British cinema. And as if to prove it, in the meantime of course they've hooked-up with the awful Irvine and become the country's most successful drug peddlers. For all its flaws, at least Shallow Grave is not yet more bum-numbing frown and grown heritage cinema, and to that we raise a (qualified) glass.