For some time I have been musing about God's name, particularly in regard to the three large monotheist religions - Judaism, Christianity, Islam.

The word god is spoken carelessly.
These religions are monotheist claiming some historical alleagiance to a guy called Abraham who 'met' their god.
So all three must worship the same god - FALSE!

The god of Islam is Allah.
The god of Jews and Christians in Jahweh.
... if you will excuse my free use of God's personal name (more commonly written LORD, JHWH or G-d).
Allah is not Jahweh - Jahweh is not Allah.

So what's in a name?
I have no recognised qualifications to speak with any authority on this but thought I would highlight a few differences between Jahweh and Allah which have come to my attention.

1) Jews and Christians can discuss the Torah because Christians have left the Torah as they received it, they share a distinctive biblical foundation.
Non-Messianic Rabinic Judaism rejects many Christian interpretations but at the core we share the same text.
Islam has fundamentally altered the Torah.

2) Both Christians and Muslims embrace continuing revelation that non-Messianic Rabinic Judaism denies.
Christians & Messianic Jews recognise the Jewish man Jesus as the King of the Jews, the promised Messiah with Jewish scripture finding its completion in Jesus.
Islam claims Judaism and Christianity are apostate. The revelation of Islam abrogates (annuls) / supercedes both - that is fundamental to Islam, not debatable.

3) One issue which separates Christians and Jews is Trinitarian theology but at the core they both declare God is One (Deuteronomy 6:4) and the revelation of scripture is that God is relational. Relationship shapes God's nature itself. God introduces himself not by his attributes but by his relationships - He is the God of Abraham, Isaac and Jacob (Genesis 50:24; Exodus 3:15; Matthew 22:32, Acts 7:32).
By contrast Allah is not described by his relationships but by his attributes - the merciful, the compassionate and (above all) sovereign.

4) The concept of sovereignty in Islam is absolute without any direct comparison in Judaism or Christianity. The will of Allah being so supreme that it is greater than the nature of good and evil, giving the theoretical possibility of Allah being able to declare evil good and good evil. This gives rise to the Islamic doctrine of Taqiyya that permits lying or concealing one's beliefs under specific circumstances.
Such a concept is inconsistent with the nature of God as both Jews and Christians understand it. Psalm 89:14 sums this up nicely by declaring Righteousness and justice are the foundation of your throne; mercy and loving-kindness and truth go before your face. In 2 Timothy 2:13 we read God cannot deny himself.

5) Both Judaism and Christianity see God's love expressed in deliverance from slavery (from Egypt, from sin) and freedom.
In Islam God's love is fully expressed by the giving of divine law (the Quran) requiring perfect submission to God and not freedom.

6) Jews and Christians share a biblical anthropology from Genesis 1:26 let us make man in our image. This is foundational to Christian social ethics. To both Jew and Christian the shedding of human blood is serious business and requires an accounting. Child sacrifice particularly is an abomination to God. In the legal codes God gave Israel after Egyptian captivity we see that God disfavoured slavery.
In Islam the extreme sovereignty and unknowability of Allah suggests that ascribing image bearing to humanity is potentially blasphemous. Although Islam does have a high view of humanity as humans are honoured above much of creation the intrinsic dignity of man recognised by Jews and Christians is missing.

7) Both Jews and Christians have a covental relationship with God, so in prayer we can appeal to God's nature (cf Psalms and Prophets).
In Islamic understanding and ethics questioning God could be seen as impious.

8) Anti-Semitism is by its very nature anti-Christian. Christians follow a Jewish bloke who is the King of the Jews, the Jewish Messiah. Christians fix their eyes on the same Jewish bloke who rose from the dead and is now at the right hand of Jahweh making intercession for them (Romans 8:34). Jahweh's relationship with the Jews is based on covenant not on behaviour. If Jahweh could annul his covenant with the Jews that easily then there would be no hope for me as a gentile. Bad behaviour has unpleasant consequences, but annuling covenant is not one of them.
To Islam both Jews and Christians are apostate (see 2 above) although their connection with Abraham requires respect. Renouncing Allah and turning to Jahweh (commonly expressed by baptism in the name of Jesus) is the unforgiveable sin and punishable by death, although fearing the law of the land may supercede fear of Allah (see 4 above).

9) Both Jews and Christians appeal to their covenantal relationship with God. For Christians this is expressed through 'assurance of salvation', knowing the presence of the Holy Spirit - Immanuel God with us. Christians look to 'the blood of the lamb', the blood of the Jewish bloke shed on the cross of Calvary (Isaiah 53:7; John 1:29).
In Islam no such certainty exists. the emphasis being on God's Mercy and his role as the perfect judge.