An answer to a previous, similar question pointed out these differences:
1) The Assemblies of God churches teach that faith is a condition of salvation rather than teaching that faith is the way God has chosen for us to receive salvation. The implication is that an unconverted, sinful human being must “decide” for Christ. WELS teaches that people by nature are dead in their transgressions and sin and therefore have no ability to decide for Christ (Ephesians 2:1, 5). We do not choose Christ, rather he chose us (John 15:16).
2) The Assemblies of God churches teach that Baptism and Holy Communion are ordinances whereby Christians declare to the world that they have died with Christ and share in the divine nature. They do not believe that the sacraments are means of grace through which the Holy Spirit works to create or strengthen faith. They deny the Real Presence in the Lord’s Supper. They insist that the only legitimate way to perform baptism is by immersion. WELS teaches that baptism and the Lord’s Supper are means of grace through which the Holy Spirit works to create or strengthen faith (Titus 3:4-7, John 3:5-6, 1 Peter 3:21, Matthew 26:26-28). We believe that Christ’s true body and blood are truly present in the Lord’s Supper (Matthew 26:26-28, 1 Corinthians 11:23-29). The Bible does not mandate the mode of applying the water of baptism.
3) The Assemblies of God churches teach premillennialism. They believe that Christ will return and reign physically, visibly, and politically for 1,000 years on earth. WELS rejects the teaching that Jesus will return to establish a political reign here on earth (John 19:36, Romans 14:17, Colossians 1:13-14).
4) The Assemblies of God churches are a perfectionist church body. According to the official website of the Assemblies of God, they believe that “by the power of the Holy Ghost we are able to obey the command: ‘Be ye holy, for I am holy.’” Holiness/perfectionist church bodies often seem to make rules where God hasn’t and to call things sinful which God has not forbidden. WELS teaches that, although we will strive for Christian perfection, we will not attain it in this life (Romans 7:14-25, Philippians 3:12). We are careful not to call things sinful which God has not called sinful (1 Corinthians 10:23-33, Romans 14:1-23).
5) The Assemblies of God churches believe that every believer is entitled to “baptism in the Holy Spirit” (an experience separate from water baptism) with the initial evidence of speaking in tongues. They also practice faith healing. They teach that such “divine healing is an integral part of the gospel. Deliverance from sickness is provided for in the atonement, and is the privilege of all believers.” WELS does not teach a “baptism in the Holy Spirit” separate from and subsequent to water baptism. We do not see speaking in tongues and faith healing as normative for Christians today.
For more detail to your question, you might benefit from A Lutheran Looks at the Assemblies of God. It is available from Northwestern Publishing House.