The President has not become too powerful, at least in relation to the powers delegated in the Constitution. The original Constitution gives the President enough power to be a strong leader, but also is open enough to interpretation so that a weaker President is also possible.
When the Constitution was first written, many anti-federalists feared that the President would become too powerful and expand his own powers beyond that of the Constitution, and that has more or less occurred. Most of the famous Presidents had, in their time, been criticized for overstepping their bounds and becoming "too powerful." Andrew Jackson, Abraham Lincoln, Theodore Roosevelt, Franklin Roosevelt and Woodrow Wilson all greatly expanded the powers of the President. While there is debate about the role of the President in the government, most of the actions taken by "powerful Presidents" were allowed under the Constitution, or were allowed under interpretations of it during times of crisis.