Planet Zebes was a playable stage in the original Super Smash Bros. However, like most other stages, (all of them except Kongo Jungle, Yoshi's Island, and Dream Land) it was not seen in Smash Bros. Melee.
Brinstar vs. Planet Zebes
There were a few stages from the original Smash Bros that were heavily modified as opposed to taken out. They were: Sector Z, Planet Zebes, and Mushroom Kingdom.
Planet Zebes, now used as the heading for Brinstar, is easily noticable as the inspiration for Brinstar.
Similarities
The two stages have severl things in common, such as:
The music is the same, only slightly remixed
There is still the yellow acid that rises and falls
They are about the same size
Differences
There are probably more differences than similarites between the two stages though. some differences are:
The acid does not have even half the original knockback
the platforms on the laft and right-hand sides can be tilted if the fleshy column is destroyed. (this regenerates over time.)
The elevator that used to be on the right-hand side is gone.
There is a group of cell-like objects, that, if destroyed, will split the platform in two.
One can fall out of the bottom blastone.