The biggest difference between the 1992 presidential election and the ones in 1996, 2000, 2004, and 2008 is that in 92 there was a viable third candidate for office, Mr. H. Ross Perot. It's not just that he existed (every election has a slew of candidates from minor parties,) it's the fact that he was polling high enough to allow him a spot in the televised debates.
In order to be invited to the debates (which are, ironically, run by the two major parties in the US through a commission,) a third party candidate must be getting at least 15% of the vote in 5 public opinion polls to be considered "viable." This number virtually ensures no-one but the candidates from the Republican and Democratic parties will have enough support to participate. In 1992, though, Mr. Perot's level of support averaged higher than that, earning him a spot.
That's the biggest difference. If your question was just taking a look at this year's election we could also talk about "SuperPAC" money, but because this is such a recent change it doesn't really relate to the extended nature of the question.