How does Qadianism (Ahmadiyyat) differ from Islam
According to the tenet of their faith, the Qadianis (Ahmadis) are required to study, accept, and follow the works, “revelations” (wahi), and writings of Mirza Ghulam Qadiani. In his books, Mirza Ghulam Qadiani makes the claim that he is in direct communication with God and ordains it upon his followers to believe in “Islam” according to his revelations. We have summarized here some of the differences between Qadianis (Ahmadis) and Muslims. It should be obvious that most of the beliefs instructed by Mirza Ghulam Qadiani contradict verses of the Holy Quran — not to mention hundreds of authentic Hadith and Islamic doctrine.
It is unfortunate that many of the people who have been tricked into accepting Qadianism (Ahmadiyyat) are unaware of this aspect of the Qadiani (Ahmadi) doctrine. Since the rituals of Qadianism resembles that of Islam and much of their terminology is stolen from Islam, many Qadianis are under the impression that they are following an Islamic school of thought. They continue to blindly send their donations to the Qadiani (Ahmadi) leadership thinking they are supporting Islam, when in reality they are helping a non Islamic cult. For the most part, the followers of Qadianism neither have a good grasp of Islam nor have access to the complete writings of Mirza Ghulam Qadiani — which are mostly written in Urdu — and are not aware of his various claims.
The following are some of the difference between Islam and Qadianism (Ahmadiyyat ):
Qadianism (Ahmadiyyat) is based on the belief that Mirza was an improved second reincarnation of hazrat Muhammad(SAW).
Qadianism (Ahmadiyyat) rejects the concept of absolute Finality of Prophethood in hazrat Muhammad(SAW), as confirmed in Quran, Hadith, Sunnah of the Holy Prophet(SAW), Tradition of Companions, the writings of Muslim Scholars and personalities, and concensus of the entire Ummah for almost 1500 years.
Qadianism (Ahmadiyyat) maintains that Mirza Ghulam Qadiani was a Prophet (nabi and rasul) of God.
Qadianism (Ahmadiyyat) rejects the concept of completion of the revelations of Allah(SWT) in the Holy Quran.
Qadianism (Ahmadiyyat) holds that Mirza Ghulam Qadiani’s revelations (Books) were on the same level as all prior revelations (Quran, Bible, Torah). In their view, simply following Quran and Sunnah, as Muslims have done since the beginning of Islam, is not a basis for living a righteous life and gaining the pleasure of the Creator. Interestingly, the Qadiani leadership has refused to allow a translation of these books, so that everyone may become familiar with the irrational teachings and contradictory claims of the founder of their organization.
Qadianism (Ahmadiyyat) rejects authentic Hadith based on Mirza’s alleged revelations and teaches his personal interpretation of the Holy Quran. Qadiani (Ahmadiyya) leadership has forged several unauthentic translations of the Holy Quran to try to confuse and mislead uninformed individuals.
Qadianism (Ahmadiyyat) teaches that Jesus(pbuh) had been crucified, but did not die from his injuries. Instead, it advocates the view that Jesus(pbuh) recovered from his injuries, escaped to Kashmir (India), where he lived for another 86 years, and is buried there.
Whereas Jesus(pbuh) is acknowledged as a great prophet of Allah in Islam, Mirza Ghulam took the liberty of making demeaning and vulgar remarks against him and his honored mother, rejected his miracles, belittled his mission and denied his return before the Day of Judgment. It is such unbecoming teachings that have resulted in hateful retributions by extremist Christians evangelical groups against Muslims, Prophet Muhammad(SAW), and Islam.
Qadianism (Ahmadiyyat) maintains that Mirza Ghulam Qadiani was “the promised Messiah”. The Qadianis (Ahmadis) reject the advent of Jesus Christ(pbuh), son of Mary, as the Messiah, just before the Day of Judgment.
Qadianism (Ahmadiyyat) teaches that Mirza Ghulam Qadiani was also the promised Mahdi (guided one).
Qadianism (Ahmadiyyat) teaches that Mirza Ghulam Qadiani was also the expected Hindu lord, Krishna.
Qadianism (Ahmadiyyat) intollerantly declares the entire manking, except for those who naively accept the irrational notions and contradictory claims of Mirza Ghulam Qadiani, to be unbelievers and bound for hell.
Qadiani leadership has announced all Muslims to be unbelievers and has forbidden its followers from wedding their daughters to Muslims, praying behind Muslims, and offering prayer on their deceased – be it a child or an adult.
Qadianism (Ahmadiyyat) teaches that struggle for freedom, independence and self-determination against the tyranny, extremism and oppression (Jihad) of those military powers that support Qadianism has been made Haraam.
At its birth, being a protoge of the oppressive British Empire of the time, Qadianism (Ahmadiyyat) required complete devotion and obedience to the British Government, as an article of faith. While freedom loving people around the globe were rising up against the British subjugation, Qadianis were being required to be willing to sacrifice their wealth, talent, and soul in the cause of the Crown. Britain is presently the headquarter of the Qadiani Movement.
Qadianism (Ahmadiyyat) holds two cities in India (Qadian) and Pakistan (Rabwah) as holy as Mekkah and Madinah. Qadianis (Ahmadiyya) are supposed to perform Hajj by attending their annual congregation, instead of visiting Mekkah.
Qadianism (Ahmadiyyat) maintains that Mirza Ghulam Qadiani was superior to all the Prophets(pbut) of Allah(SWT).
Qadianism (Ahmadiyyat) refers to the companions of Mirza Ghulam Qadiani as Sahaba and his wives as Mother of the Believers (Ummahatul Muminin).
Qadianism (Ahmadiyyat) advances the notion that many verses of the Holy Quran were revealed to Mirza Ghulam Qadiani and that many of the praises of Prophet Muhammad(SAW), mentioned in Quran, were really intended for Mirza Ghulam Qadiani.
Qadianism (Ahmadiyyat) claims Mirza’s Mosque at Qadian (India) to be Masjid-ul-Aqsa.
References to the Qadiani books requiring these beliefs are provided on various articles at this site. If you have been tricked into accepting Qadianism (Ahmadiyyat) without being told of these and other truths, please be assured that our quotes are based on authentic writings of the founders of that organization. What you have fallen in love with is Islam and not Qadianism. The door of salvation remains open to all, but you will need to take the first step, you must be seeking the truth to receive guidance.
Has not the Time arrived for the Believers that their hearts in all humility should engage in the remembrance of Allah and of the Truth which has been revealed (to them), and that they should not become like those to whom was given Revelation aforetime, but long ages passed over them and their hearts grew hard? For many among them are rebellious transgressors.
(The Holy Quran, Al-Hadid, 57:16)
We beseach Allah(SWT) to guide all sincere individuals to the right path and save them from the mischievous ploys of the enemies of Islam. 
 How does Qadianism (Ahmadiyyat) Differ from Islam: http://irshad.org/qadianism/differ.php