The american system is fine. The constitution, bill of rights and most of the voting system is just fine. I don't like the "first-past-the-post" style system, and I would prefer if the US adopted a preferences system like we have in Australia, but apart from that I've got no real problem with the American government, as it is supposed to theoretically operate.
What I have a problem with, and this goes for just about every single nation out there, is the people. I include myself in that group as well (so this is also self-criticism).
The US population could demand genuine bipartisanship. It could reward politicians for reaching across the aisle, for passionately pushing his or her principles, informing the general public as well as for making sensible legislation.
But no. That doesn't happen. If you reach across the aisle, you're a traitor. If you compromise, it means you're weak-willed. If you try to pass legislation that will hurt any group of people, even if it's unavoidable, they will complain.
But at the same time, if you TELL the people that you are doing what they want you to do, if you say the sound-bites and repeat the lines at the appropriate times, the vast majority of the American people will vote for you.
It's remarkable - you Americans have a wonderful system of government. The US government has to, by law, put forward all its policies for the people to scrutinize. You genuinely have the power to punish or reward officials for their behaviour. And you don't. You can't be bothered. It's too much EFFORT to drag yourself to the voting booth ONCE every FOUR YEARS (or once very two years if you count mid-terms). It's too much effort to actually do research on what your politicians are saying.
But its easy to demonize the opposition, so you do that. It's easy to make issues BLACK OR WHITE so you do that. It's easy to demand that politicians obey your every whim, even when it's impossible, because YOU don't have to make the policy. It's easy to demand, when you don't know, or don't CARE to know, the constraints your government works under.
The problem is with the People - loud, angry, ignorant, impatient, hyper-critical, and selfish. This isn't just Americans - this is the general population of every major nation.
But don't let this get you down - it's ALWAYS been like this. And despite it all, the US has thrived, and time and time again it's been your system that has saved you, you didn't save your system. I gather the majority of Americans, throughout your history, would eagerly elected a dictatorship if your laws allowed it. Thankfully, they don't. Your laws force you to be free and civil to each other, and you can thank your founding fathers for that. They made such a great system that even human nature has trouble destroying it.