Krugman on the plan:
The short answer: to appease the centrists, a plan that was already too small and too focused on ineffective tax cuts has been made significantly smaller, and even more focused on tax cuts.
Of course, read the whole thing: http://krugman.blogs.nytimes.com/2009/02/07/what-the-centrists-have-wrought/
In contrast to Krugman, I think Obama will be able to go back. As a matter of fact, I think he was always going to need to go back. For one thing, the problem is way too big for one measure to address it all. For another, adjustments will need to be made. And third, I think the timescale we're working with will be so long that multiple dips will be needed. The 2001 recession took almost four years to work through. This one is only a year in, and seems to be much more serious, so the only real question is whether we are on our way out of it by the end of Obama's first term.
I don't think Obama is necessarily in trouble even then, so long as he is seen as having been trying to do something and if he manages to have even some local successes. FDR won re-election even though he hadn't seen a recovery (or even made it worse, if you believe GOP 'history'). Obama may very well win again even if the economy is still in the crapper because the Republicans (like their 1930-era forbears) can only win if they have some new ideas to offer!
If there's anything the Republicans have shown a dearth of, it's new ideas.
Until they think of some, the country will stick with Democrats, regardless of their success or the lack thereof.