If anything, Stage 9 proves just how much of a mature game Metal Gear Solid is.
In a time when everyone was playing Pokemon, Metal Gear players were treated to a pyro manic who commits suicide, your team of friendlies starts to think there is a betrayer amongst themselves, and there is a little backstory on how one member of your team killed his own brother while another talks about the illegal drug trade of that area.
Stage 9 has players blowing up the entire power plant instead of just the power turbine by using four strategically placed C4. Snake is forced to blow the place while he is still in it to prevent Metal Gear from launching another nuke and a Metroid-style countdown timer haunts the player while the exit is found in the debris. A dramatic and entertaining stage.