The PlayStation port is noted for its faithfulness to the original arcade experience.
Unlike its predecessors, simply surviving to the end of a stage isn't always enough to progress to the "best" ending.
: Critical breakdowns of its difficulty and "wacked out" levels can be found on specialist retro sites like The OPCFG . SEXY PARODIUS REVIEW - The OPCFG
: You can find full no-commentary playthroughs on YouTube to see the mission branching in action.