What do think how big meaning it's for developing the life on Earth, that gravity is just 1 G.

 

Small differences would surely have been disadvantage to developing of life, but what would be the appearance of creatures on the planets with f.ex. 0.5 G or 2 G.

I think you should define it other than in terms of 'g' (that's LITTLE g, big G is the gravitational constant), given that g is defined as 'the gravitational attraction of the earth at sea level'

 

If g were smaller, I'd say life would tend to be taller and thinner, and the opposite were it larger.