The reason you think that the film is highly over-rated is because it's been duplicated so many times. Interesting dialogue, wonderful acting, unconventional camera shots, and suspenseful scenes wrapped around a storyline that does not force feed you information. That's why you're not told what's in the briefcase. That's for you to decide. Although the main belief is that the suitcase contains the soul of Marsellus Wallace, but other ideas are that the suitcase contains Tarantino's first Oscar, the Elvis suit from True Romance, among other ideas.

Watching the movie for the first time today would not be the same as watching it when it was first releashed. The techniques used by Tarantino have been copied numerous times and I could name a dozen movies that should grant credit to Tarantino. But, to be fair, Tarantino himself 'stole' his techiniques from other directors but puts them together in a way which makes his film unique.

A much better review of Pulp Fiction can be found here by none other than Roger Ebert.

I hope this puts the movie in better perspective.