As many observers have noted, the proposal would give unchecked financial power to the Treasury Secretary, something that seems particularly unwise and certainly undemocratic.
The criticism is bipartisan. Here, from page on of USA Today, are a couple of choice quotes from different political perspectives:
This massive bailout is not a solution. It is financial socialism and it's un-American.--Sen. Jim Bunting, R-Kentucky
After reading this proposal, I can only conclude that it is not just our economy that is at risk, Mr. Secretary, but our Constitution as well.--Sen. Chris Dodd, D-Connecticut, to Secretary Paulson