It depends on a few factors.

The biggest one being why it's flaccid and/or has runny cheese - Some pizzas are just greasy and lead to flaccid crust/runny cheese. And a greasy pizza isn't necessarily bad.

Just like a burnt hot dog isn't necessarily bad either. Seriously - a somewhat burnt hot dog can be delicious depending on the circumstances - just like an ice cold beer hits different outside on a hot day.