This work highlights the effects of nonlinearity during the formation of large wave events in both infinite and finite water depths via extensive fully nonlinear numerical simulations of focused waves. The results indicate that the shape of large waves varies both in crest elevation and in crest width, with varying degrees of steepness, water depth and directionality. Large steepness leads to larger crest elevations and wider crest widths. As the water depth becomes shallower, the crest elevation reduces but the crest width increases. A decrease in directional spread leads to a decrease in crest elevation. The further physical understanding of this behaviour is provided by the application of a harmonic separation scheme.