This thread may not last long...
These religions have nothing in common. Just because they start in the same place does NOT mean they have similarities. The definition of religion is a set of beliefs, and only one can be correct (or none, if you want to get into messy theological debates). If that's the case, then that means they don't have any meaningful similarities because they are polar towards each other.
The Quran is said to be 'bad poetry'. The Old and New Testament are attacked as being inconsistent with each other. Judaism (or some branch, anyways) is claimed as being old-fashioned. The fact of the matter is, they all have criticisms of each other that are unavoidable, no matter what your stances are. Thus, finding similarities is just political correctness and nothing else...Protestants and Catholics hardly have similarities save for the core beliefs.
God Himself is not even portrayed the same in the three...or close to it. Okay, so he created the world...yeah? I think Amun Re (or however you spell it) did that, too. The Old Testament God (Judaism) is of harsh ultimatums; if you don't obey, you'll be a pile of salt or blinded. If you do obey, your children will live and entire cities will fall to your soles. And the instructions he used nowadays are seen as silly...put a red string/chain/something up for something (I forget the specifics)? Okay, that's weird...kill Sisera (I think it was him..) with one of his tent pegs into his temple...uh-huh, thus stuff makes a lot of rational sense.
I'm just pulling this from an old teacher, but, if I recall, his portrayal of Allah is this: "You love Allah, so Allah will love you." An eye for an eye? I don't know; I'm no expert...
The Christian God is more complicated, with the Old Testament persona plus, essentially, his tri-nature, which are essentially different jobs the one entity has; it's like wearing masks. Think--do you act the same at school as you do at home? How about at your friend's house? How about at that fancy French restaurant? Oh, no...you're one person but can wear many different guises; that's the nature of the Christian God. If light can act as a particle and a wave, then why can't God act as a sanctifier, creator, and redeemer without being seen as different pieces? Light is not different things...
Judaism and Christianity themselves have enough quarreling (but no real 'wars' like the Jews and Palestinians) considering the Christians have their Messiah while the Jews are, even while I type this, waiting for the first arrival of their Annointed One. They have nothing in common; this is like saying capitalists and communists should bear hug each other and share a cherry pie. It just doesn't happen; yeah, they agree that we shouldn't be in a barter system, but they disagree over the most fundamental pieces of things...
Do these Gods have anything in common? Other than the generic creation motif, not really...the rest of the religions fall underneath that; if the core beliefs don't agree, then there ain't much connecting them. Otherwise, you had better be prepared to add in Germanic pagan religions, Eastern religions, and others...they all originated on Earth and do their best to explain the start, finish, and nature of our world, don't they?