First, let me preface this by saying that some generalizing is necessary for a reply to such questions. What I say is not meant, then, to be taken as a description that is always accurate (there are exceptions to most "rules"). I will try to avoid being polemical if I can, and I will definatley avoid politics 
Some Differences...
ROCOR is much stronger in its stance against false ecumenism than other groups. ROCOR has even anathematized certain theories popular among some (non-Orthodox) ecumenists, such as the "branch theory".
ROCOR has, for the most part, stayed out of the mire of modernism. Many other jurisdictions have sunk down into this mire, some to a lesser, and some to a greater, extent.
ROCOR tends to be more ascetical in practice, which means many ROCOR Churches are without pews, fasts are expected to be kept, a fuller liturgical life is done at the parish, etc.
ROCOR is also different because it is one of the few groups in America who embrace their ethnicity (though, of course, they don't exclude other ethnicities from participating with them). Many Churches like the OCA and Antiochians are trying to be (or move towards) an "American Church". ROCOR, on the other hand, considers itself to still be a Church of Russians who are dispersed throughout the world. It should be noted that ROCOR keeps it's ethnic roots and customs in an acceptable way, and that they do not fall into the wrong kind of ethnic or national focus, something which has been condemned.
ROCOR continue to use the "old calendar," as was pointed out earlier. The issue of the old calendar is as much one of modernism as it is dealing with the actual calendar. The traditionalists such as ROCOR see the original acceptance of the "new calendar" as a lapse, and a concession to false ecumenism/modernism.
ROCOR is, on the whole, more faithful to the canons of the Church (e.g., from Councils) than many other jurisdictions are. Even members of the other jurisdictions have made that observation over the years. What this means is: 1) ROCOR sometimes seems like legalists, because some believe that certain canons are not applicable today; and 2) the faithful (laity) of ROCOR are protected from error to an extent by the clergy's conservative approach.
ROCOR continues to speak out against theological errors such as Sergianism and the "canonization craze" that is effecting some groups (the "craze" spoken of is the over-zealousness by some in one particular Church to canonize a number of people who were obviously not Orthodox saints).
ROCOR has steered clear of all of the modern ecclesiological errors that are beginning to infect some other jurisdictions. Neo-papal-partriarchalism and officialism are two of the more common cerrors.
If you do a search on Google for all these terms I'm mentioning, you'll undoubtedly pull up many pages. I don't mean to leave you hanging here with a bunch of funny words you've never heard of before. It'd just take too long to go over all of them at once.
If you had specific questions, though, I'm sure many on the forum would be happy to try and answer them. 
Justin
PS. When I said that ROCOR embraces it's ethnic roots, I hope this doesn't scare you away! I'm an American, but I am still becoming ROCOR. The ethnicity will only "get to you" if you don't mesh well with the culture, for whatever reason. The ethnicity in itself isn't really a hinderance, though 