the biggest restriction, in my opinion, on the federal government was the nothing could be passed due to the senate being controlled by state legislatures.
Which, of course, is why the Progressives were staunch advocates of direct election of senators and got the 17th Amendment in annus horibilis (1913, the year that the US got the federal income tax, direct election of senators, the Federal Reserve, and President Woodrow Wilson).
By the way, a reasonable reading of Article V yields the conclusion that 17th Amendment should be considered invalid: "no State, without its Consent, shall be deprived it's [sic] equal Suffrage in the Senate." Ten states never ratified the 17th Amendment, thus losing their Suffrage without Consent. But that's just more evidence that the entire Constitution is a dead letter.