At this point in time, I think anyone who thinks that there is a dramatic difference between the Democrats and the Republicans on most issues (or in how they would govern) is very naive.
Now, Obama has disappointed a lot of progressive voters because they believed he was very progressive (and he may be) and he had every opportunity to do whatever he wanted but he failed to achieve a fraction of what they expected. The reason for this is simple, there are so many special interest groups with conflicting objectives that "own" most of the Democrats in government it is nearly impossible to get something meaningful passed; and this isn't any different from the Republicans, except that they have a different group of special interest groups with conflicting objective that "own" them.
