Even though there were significant differences in campaign rhetoric between the two major party presidential candidates, on policy post-election there has been very little real daylight between the stated positions of McCain and what the Obama administration has actually done. The entire American Left has thus been effectively unrepresented in the current political dynamic. When a Democratic administration effectively promulgates Republican policy it pretty much forces the party to either fall into line and support that policy or engage in fratricidal intraparty war. A Democratic party in opposition would have been obliged to oppose many of the Republican policies it has been forced to support in the name of party loyalty, a healthier political dynamic I would assert than having two parties in putative opposition operating on the same ideological turf.
Besides, the ongoing failing economy under a McCain administration would have seen the blame fall squarely on its real cause- supply-side Reaganomics and continued plutocratic looting of the American economy- rather than handing the crazies on the Right the fictional narrative that the economic collapse was caused by a "socialist" set of principles. Four more years of Republican economic policy under its proper name would probably have discredited and killed the whole supply-side voodoonomics brand once and for all. Instead because the whole supply-side plutocratic theft agenda was essentially taken up and run with by the Obama team, it is still alive and will continue to destroy the American economy regardless who wins in 2012. The Obama victory spared the Republicans having to own the abject failure of what should rightly be their economic policies. Four years of McCain/Palin after eight of Bush/Cheney combined with an economy in free fall brought on by essentially the same failed economic policies we wound up with under Obama would probably have comprehensively destroyed the Republican Right-wing brand for the foreseeable future.
Additionally, under a Republican administration the Democrats would likely have been forced to bring pressure to bear to look into the crimes of the previous administration: illegal war, torture, renditions, FISA abuses, warrantless wiretaps etc. rather than taking the shameful and I would assert criminal path of "looking ahead" and leaving the ugly and immoral precedent of the outrageous criminality of the previous administration with its incalculable damage to the rule of law and our Constitution to stand unexamined and unrefuted.
A Right-wing Democratic administration is the worst of all possible worlds. It has almost all the downsides of a Right-wing Republican administration with the additional downsides of letting the Right off the hook for the inevitable failures of those policies, the almost total suppression of any organized opposition to those policies and the general killing of almost all progressive policy initiatives within the Democratic Party. Under Obama the center of political discourse has been allowed and even pushed so far Right that the truly crazy Right has been brought into it and there is nobody in power with the principled ideological standing to make sane counter-arguments. The current political dynamic has marginalized liberal political thought and empowered conservative ideology.
Would we have been better off still with a liberal Democratic president or an Obama who honored his liberal-progressive campaign rhetoric with action? Of course, but that obviously was never an option. So yes even considering the downsides, the Democratic Party and America would have almost certainly been better off looking forward if we'd had a Right wing Republican administration rather than a similarly Right wing Democratic administration. Which is I'd assert exactly what we wound up with.