Oftentimes, strong soundtracks tie musical motifs to in-game themes. This is what gives the music its memorability and strength. Modern soundtracks do sometimes eschew the use of motifs for a more grandiose feel, or simply for a set of standalone songs; while these techniques may be simpler, they don't always lead the relative emotional hooks gained through the solid use of motifs.
Not saying modern soundtracks are worse or better, but it's worth noting that, as everyone's saying, nostalgia will act as inherent sample bias; your thesis is already pretty skewed towards a specific conclusion. Try to find sources among professional composers, if you can, as well as within other game communities, especially ones that aren't focused on music. Also try to tweak the thesis, and approach the paper from a neutral direction. Let your findings direct the paper's tone, not the other way around!