Details here. An excerpt:
"[. . .] the G.O.P. plan turns out not to be serious at all. Instead, it’s simultaneously ridiculous and heartless.
How ridiculous is it? Let me count the ways — or rather a few of the ways, because there are more howlers in the plan than I can cover in one column.
First, Republicans have once again gone all in for voodoo economics — the claim, refuted by experience, that tax cuts pay for themselves.
Specifically, the Ryan proposal trumpets the results of an economic projection from the Heritage Foundation, which claims that the plan’s tax cuts would set off a gigantic boom. Indeed, the foundation initially predicted that the G.O.P. plan would bring the unemployment rate down to 2.8 percent — a number we haven’t achieved since the Korean War. After widespread jeering, the unemployment projection vanished from the Heritage Foundation’s Web site, but voodoo still permeates the rest of the analysis.
In particular, the original voodoo proposition — the claim that lower taxes mean higher revenue — is still very much there. The Heritage Foundation projection has large tax cuts actually increasing revenue by almost $600 billion over the next 10 years.
A more sober assessment from the nonpartisan Congressional Budget Office tells a different story. It finds that a large part of the supposed savings from spending cuts would go, not to reduce the deficit, but to pay for tax cuts. In fact, the budget office finds that over the next decade the plan would lead to bigger deficits and more debt than current law. [. . .]"
UPDATE: See also Richard Posner's critique of the budget plans here.