Yes, besides being the simplest religion, Islam is also the most rational religion of the world.
The following facts have made Islam to be the fastest growing religion of the world:

• God is One. The concept of God in Islam is very simple, clear and precise. There is only One God, Who has created the entire universe and everything in it. He Alone is worthy of worship.
• God does not have parents or offspring. God is far above the worldly attributes.
• All Messengers, deputed by God to carry His Message to mankind were humans, who lived and died like humans. God had bestowed some of them with miracles.
• There is no clergy in Islam. Islam does not require any priest or any other intermediary for carrying out any of its acts of worship. Islam establishes a direct relationship between individuals and their Creator.
• Islam is the only religion to reject the idea of celibacy to receive the pleasure of God. Every normal act of life of a Muslim becomes an act of worship, if done in a manner that pleases God. 
• Islam treats all its followers alike irrespective of the color of skin, nationality, educational levels or social status etc.
• Islamic principles are extremely simple to follow and are very rational and logical.
• Islam is the first religion to recognize, define and practice human rights more than 1,400 years ago.