Why is water liquid where as H2S is gas at room temperature?

Because there is no hydrogen bonding between molecules of H2S.

Oxygen is a very electronegative element, so in the O-H bonds, it draws the bonding electrons towards it, making one side of the molecule more positively charged than the other.

In water, the slightly negative side of one molecule (the oxygen side) will be attracted to the slightly positive side of an adjacent molecule (it's hydrogen side), forming an intermolecular bond called a hydrogen bond.

Sulphur is less electronegative than oxygen, so doesn't draw electrons to itself in the same way, meaning that H2S molecules are more neutrally charged across the whole molecule, and so hydrogen bonds don't form and the molecules aren't as tightly held to each other as they are in water.

Note: It's important to distinguish between intermolecular 'hydrogen bonds' and O-H or S-H bonds within molecules.