Oddly enough, much as I love Mr Tarantino's movies generally, I can't enjoy Reservoir Dogs because I find Tim Roth too annoying. I think it's the accent.
I enjoyed him in Pulp Fiction though. Did he use his own (or at least a British) accent in that?
By the same token, I couldn't watch JFK for years because Kevin Costner just looked and sounded ridiculous to me. I eventually got over that one and now consider it a reasonably good film.
I think it's more a personal preference thing than bad performances though.