It depends how different your levels are. If they're similar (as in, the way they play) then you could probably get by with one 'game' loop. Before the loop begins, you would run a unique gosub (or do something similar, like load a unique array) that would set up the terrain/items/characters for the current level.
If your levels are completely dissimilar, I would advise using "goto" commands, but it's really a matter of personal preference, I think.
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