Alpha emphasises the infilling of the Holy Spirit without adequately making sure that the recipients are actually converted. Alpha has a very scant doctrine of God. It is extremely man-centred, focusing always on our needs and problems, not on the will of the Almighty God who must be obeyed. There is little or no explanation of God as the Creator and the Fall of Man. Alpha stresses love and acceptance and underplays God's holiness and His wrath with our sin.
Sin is described more in terms of something that messes our lives up.
Hell is not mentioned by name. Alpha does not explain why Jesus had to die, because it does not preach the law of God, or show how angry God is at our breaking of it. Jesus' death is reduced to a great example of self-sacrifice. Alpha's official publicity material promotes testimonies of people whose first real experience of spiritual things comes during the Holy Spirit weekend, not whilst hearing the preaching of the Gospel. These are New Age experiences, and very little to do with hearing the Good News of the Lord Jesus Christ, repenting of sin, believing on Him, and being saved.