Like many questions, the right answer is probably, "it depends." Whether ETFs are the best investment vehicle for a particular person likely depends on their goals and needs. However, with trillions of dollars being held by ETFs, their size has necessitated a broader discussion of their merits. This is particularly true in light of recent pricing issues where ETFs traded well below their NAV (such as in August of this year, as well as during the "flash crash" in May 2010). See a good summary article here: WSJ.
Dolvin, Steven D., "Are ETFs Good or Bad?" (2015). All Chapters. 147.