Evidently, whether you’re “disappointed” with Obama or not depends on the baseline. I do agree that, compared to other actually existing presidents, his record can’t be considered disappointing at all — somewhat better than Clinton and vastly more accomplished than Carter. And comparisons with LBJ and FDR do indeed tend to understate the more favorable contexts they were dealing with and (at least in the latter case) tend to airbrush the very substantial errors of his presidency.
But I also don’t think that past presidents should be our only baseline. I agree that it’s stupid to criticize Obama for not accomplishing things that were impossible to accomplish (single payer is here if you want it!) But it’s perfectly reasonable to be disappointed in the major failures that were under his control — such as his abysmal civil liberties record — even if it’s true that previous presidents have generally been as bad or worse. Historical perspective is important, and is important to consider when entertaining fantasies that throwing one more election to the Republicans will finally restore the Really Progressive Democratic Party that never existed — but we should also always be expecting more. I don’t think Obama should be exempt from criticism for his actual failures any more than LBJ should be given a pass for Vietnam or FDR for the internment. Some disappointment even in better-than-typical presidents is a good and necessary thing.