The Articles of Confederation (AOC) crucially lacked the authority to raise revenue through taxation, or coin money, and thus could not fund a well-trained or well-equipped army, or create a navy. The Articles of Confederation did create a unicameral legislature, as opposed to the bicameral one later created by the Constitution (with the Senate and House of Representatives), but this unicameral body lacked the ability to raise revenue and appropriate spending. Consequently, the legislative body created by the AOC was extremely limited in its ability to govern.
Luckily, the Articles of Confederation did appoint George Washington as the head of the Continental Army, but it did not create an executive branch of government, so it lacked a clear leader who could mediate differences that arose within the single legislative branch. That said, this kind of mediation was less necessary with regard to the AOC, since the AOC's main objective was to unite the colonies for the purposes of fighting the British, and not to create a new government. In fact, it was not clear at the time that the delegates from the thirteen colonies truly wanted or needed a strong central government. This is perhaps the biggest difference between the AOC and the Constitution. The former was a quickly drafted agreement meant as a placeholder to help the colonists organize their war effort, whereas the Constitution was drawn up after the war had ended, and the business of governing a new nation was paramount.