As the Founding Fathers were creating a structure for a new government, one of their primary concerns was prevention of all governmental power from being concentrated in any one person or body. They very purposefully chose to create a format that is not efficient in the sense of being able to act quickly with minimal discussion and debate. They were much more concerned with the effectiveness of the government in allowing for representation of the citizens in the process.
Efficiency is not necessarily a good thing. Sure, if the executive branch had all the power things would get done. But they would be the things the executive wanted to get done, not the people. What was done would not necessarily be best for the people. It's called a dictatorship.
A system without checks and balances isn't a democracy or a republic as we know it in the United States. I agree with the above post -- more efficient yes, but better? I don't think so. Approaching the issues of our nation and our lives from multiple perspectives takes time, but in the overall assessment, our system works as it should. People around the world want to come to America to live under this system, so there must be something admirable in it.
Absolutely, it would be more efficient and effective. Just look at the way things are today. We have Democrats controlling the White House and sort of controlling the Senate. We have Republicans controlling the House. So nothing gets done as our problems get worse. A single branch with one party in power would obviously be able to get its agenda enacted without problems.
Now, the real question is, do we want to have a government that is more efficient or do we want one where it is harder to get anything done so that A) the government can't tyrannize us and B) hopefully policies that pass are better thought-out because they had to go through a harder process to get passed?