In this thesis we discuss three separate analysis of various phenomenological aspects of heavy-ion collisions (HIC). The first one is a possible generalization of the kinetic theory framework for dense systems. We investigate its long-time behaviour and the properties of the equilibrium. The second discussion is about the phenomenological analysis of the azimuthal asymmetry of the particle yields in a HIC, where we link the initial stage geometrical asymmetry to the particle yields and examine the possible organizing mechanisms that could be responsible for such a relation. The third, and also the most thorough part of the thesis is about the relation of the spectral density of quasi-particle states and the macroscopic fluidity measure (the ratio of shear viscosity and the entropy density) and other transport properties of the system. We extensively study the liquid-gas crossover with the help of model spectral functions. The main conclusion is that the relative intensification of the continuum of the scattering states compared to the quasi-particle peak makes the matter more fluent.