In most cases (The Hunger Games, Twilight, The Hobbit, etc) i agree, but I actually quite liked it with Harry Potter. It did leave Part 1 with a somewhat unsatisfying ending (though i enjoyed the rest of the film), but it also meant that Part 2 was able to wrap the series up without it feeling cramped (my biggest complaint towards 1 through to 6). I'm totally fine with that compromise. Looking at how much money they made ($2.3 billion~ in cinema revenue), and the generally positive reaction from fans and critics towards both films (though part 2 in particular), i'd say they made the right call.
I'm going to wait until both parts of Infinity War are out before judging that. Every major 2+ parter up until now has been adapted from a single book, where a lack of content (such as with the Hobbit) can result in all of them feeling unnecessarily slow or being packed with filler. That shouldn't be a problem for IW, so the end result could be completely different.
