In the SOTU, President Obama proposed an increase in the minimum wage, controls on greenhouse gases, gun control legislation, and increased spending on public works (amongst other things). Whether you agree with him or not, in each of these cases you can identify (a) the problem which President Obama is concerned about and (b) the way in which the proposed policy fixes addresses the problem. In most cases it's easy to connect the problem and its solution to the lives of regular people (though not so much in the case of climate change, perhaps).
But the response speech? Reducing the deficit exclusively through spending cuts. Block-granting Medicaid. Eliminating "excessive" regulation. A common feature of these proposals is that none of them has any direct connection to any problem experienced by any American in the course of their lives. The Republicans are reduced to arguing that, through some unspecified mechanisms, these policies will improve our lives as a kind of side effect of the policies themselves (though again, the exact improvements which we are to expect are generally not stated explicitly).
Similarly, the Republican argument against Democratic Party policy proposals is generally that they will result in more harm than good, again as side-effects and in ways which are generally not specified. Increasing public works spending will "increase the deficit." So what? The Republicans don't say, but imply that it will cause economic problems. Raising the minimum wage will cause employers to hire fewer people and/or fire more people, offsetting its effect on improving the lives of people living with minimum wage jobs.
It's not just Rubio or the response speech, either. Thinking back to the Presidential campaign, my recollection is that it was a similar situation: the President proposing policies which were at least designed to address real problems in a clearly-understandable way; Governor Romney responding by asserting that cutting taxes on high earners, cutting government spending, etc, would make everything better for everyone via some unspecified mechanism.
Which leaves me with a question: What are the Republicans really offering anyone these days? How are their supporters supposed to get behind their mushy proposals which connect to everyday lives only in the most abstract way imaginable? At the risk of dating myself here: where's the beef?
The rejoinder to this would be that this is precisely Republicans' point. They're not proposing more services or subsidies or government programs. They want to cut it, reduce its intrusiveness, reduce its cut of your paycheck. The problem, I think, if it is a problem in political terms, is that that message makes much more sense in a very different political setting -- one in which taxes are much higher, regulations are much more cumbersome. This is why they're reduced to arguing against a fictional Obama who's well to the left of George McGovern. Because it's only in that context where a lot of these arguments make sense.