Did all ancient civilizations share a common attitude about the nature of their divine beings and their relationship that these gods had with...

Absolutely not! Indeed, it's not clear that even within a civilization there was anything like a consensus on the nature of the gods.

Still, there are certain patterns we tend to find, and some interesting comparisons and contrasts we can make between these three different ancient texts. The hardest one to get an unbiased source on is of course the Old Testament; European and American culture is pretty heavily invested in the Bible and its interpretation. I decided to just link the full text.

All three texts appear to assume some form of polytheism. This is one of the things about the Old Testament that can be very controversial, so let me explain further: A number of passages in the Bible clearly indicate the existence of other gods, and simply place Yahweh on top---not the only god, but the best god. (This is sometimes called henotheism.)

For example, Psalm 95:3; "For the Lord is a great God, and a great King above all gods." Another example is Deuteronomy 6:14; "Ye shall not go after other gods, of the gods of the people which are round about you;"

The Bible was written over a very long time by a lot of different people, so there are other passages that do insist that there is only one god, such as Isaiah 43:10; "before me there was no God formed, neither shall there be after me." These passages tend to be from books that were written later, suggesting that the Jews gradually transitioned from polytheism to monotheism over time.

The gods are clearly literal beings in the Bible and the Epic of Gilgamesh, but in the Iliad this is not quite as clear. One reading is that yes, they are literal gods which actually help or hinder each side; but another reading is that they are being used as metaphors for the properties that are associated with each god, so for example summoning an idea from "Athena" really means summoning it from wisdom, and acting based on the will of "Ares" really means acting out of warlike rage. There are a few passages in the Iliad where this second reading is a little harder to accept, but for the most part it actually holds up surprisingly well. It may be that Homer (or whoever wrote it; we really know next to nothing about Homer) did not actually believe in literal gods and simply used them as literary devices; or it may be that he actually believed in them and thought they interacted directly with human affairs.

Major characters in both the Iliad and Gilgamesh are depicted as the children of divine beings---namely Gilgamesh himself, the son of Ninsun, and Achilles, the son of the sea nymph Thetis. There is no such character in the Old Testament, though of course according to the New Testament written hundreds of years later, Jesus is the son of God.

The role of the gods varies a great deal between each text. In the Old Testament, Yahweh is the creator of, well, everything---the heavens and the earth. But in Greek myth, including the Iliad, Zeus didn't create anything in particular; the beings that created the universe were Titans, and they are long gone, defeated in a war against today's Olympian gods. The Sumerians did have creator gods, but in Gilgamesh, the creator gods don't get a lot of attention. There are a whole bunch of gods more directly responsible for administrating the universe, and they get a lot more "screen time" as it were (especially Ishtar, who attempts to seduce Gilgamesh and is scorned).

Yahweh in the Old Testament is a self-contained deity, a single being who acts upon the universe more or less unopposed; if other gods exist they are all much weaker. There are no apparent limits on his power. As said in Job 42:2; "I know that thou canst do every thing, and that no thought can be withholden from thee."

But in the Iliad, most of the gods are fairly evenly matched, and they take sides; Athena and Aphrodite are on opposite sides in the war, and it's not clear from the outset which one will prevail. Zeus seems to be more powerful than the others, but it's unclear how much, and he certainly does seem to be limited in what he can do by himself. He often acts as a kind of judge or arbitrator between the other gods.

In the epic of Gilgamesh, on the other hand, there are many gods that seem evenly matched, but they don't take sides in the same way. When all the gods want something, it happens---including, importantly, the death of Enkidu. In some ways the gods seem like a sort of court or legislature for the universe; they vote or reach consensus on what is supposed to happen, and then it happens. This is particularly true of the "seven gods" who make the decrees of fate (of which Ishtar is one).

In general, I think these ancient texts are most informative about what their authors thought about the gods, and what they thought their readers would relate to---and not necessarily the views of their entire civilization. Just as today there are different sects and denominations with different interpretations of religion, in ancient times there were as well, if anything more fragmented because transportation was so difficult and literacy was so low. It was quite common for particular villages to have their own gods, and often have little or no knowledge of the "Greek gods" or "Sumerian gods" that ostensibly held sway in the region. (Very few people at the time even thought of themselves as "Greek" or "Sumerian"; the Iliad is actually historically important because it is one of the first texts to really link various city-states such as Athens and Sparta into some kind of united "Greece".)