It didn't make that much of a splash. It was more of a slow burn. Search for it. As for "insipid and flat" compare it to, say, The Usual Suspects (a year later) or Silence of the Lambs (4 years earlier) or Goodfellas (4 years earlier) or Sneakers (3 years earlier) - or shit, Reservoir Dogs or True Romance. Story-wise, it's weaker than all of the above. Gimmick-wise, it's much, much thicker. In the end, it's only opinion - but in my opinion, Pulp Fiction is a grossly overestimated film. Spin Magazine once did an article entitled "top 10 albums owned by people who hate music" or the equivalent. Pulp Fiction is much loved by people who watch a lot of Reality TV.
I think I concede your point. Help me out though: you say Pulp Fiction is gimmickier than all the above, and I agree, except I don't know exactly why. True Romance feels a more genuine, single-entendre film than PF, which feels more self-aware.. Or something. I think my lack of film knowledge and vocabulary are showing. So what makes PF (more) gimmicky?
Smoke and mirrors. A movie about a shark that keeps throwing up people until they have to open a beach sounds like some sort of magical shit, but it's just Jaws backwards. Jaws forwards is "Roy Scheider enlists Richard Dreyfuss and Oliver Reed in killing a shark puppet." But Roy Scheider, Richard Dreyfuss and Oliver Reed are f'ing fascinating killing a shark. They're fuckin' dope at it. There are no song'n'dance numbers, there's no basement full of gimps, The Wolf does not show up in an NSX for the express purpose of giving the director a cameo. The Usual Suspects has a lot of smoke'n'mirrors, too, but you have to watch it cynically to see them. There are a lot of blind spots that are well-hidden from the audience but as soon as you peer Sneakers or Silence of the Lambs, on the other hand, are straight-up linear storytelling with no hidden gotchas, no obvious shit hidden behind mirrors, nothing funky to disguise a thin narrative. On the other hand, Pulp Fiction is an ensemble film about tied-together narratives that disguises the fact that nothing really happens, nothing is advanced, nothing is lost, and nobody has any stakes by throwing the whole thing out of linear time and substituting plot with violence and wise-cracks.