Waterfall (as a bad management practice, which sadly is still practiced) is bad when you're trying to run a large scale project and don't have feedback (because Waterfall does not include feedback). Waterfall-the-real-thing has no feedback loops built-in or severely delayed feedback (months of dev followed by months of testing, I'm watching my colleagues across the hall repeat this mistake right now, they "finished" dev last week but it won't be installed for the testers until the fall and they've started developing their next version of the system...morons). If you actually have biweekly feedback, you don't have Waterfall.

Planning and then executing on that plan in short increments is reasonable. Planning and executing on that plan over months or years, stupidity and insanity.