This is the last film that the stars are signed to via contract. They've all said that they'll come back for #4, but only if Sam Raimi directs. Sony Pictures, on the other hand, has openly stated that there will be more Spider-Man films... with or without the principles.
Critics piss me off because they're paid to offer their opinions, but seldom have little to no actual experience with doing it themselves. How many movies has Ebert directed or starred in? Roeper? And yet all they do is sit back and hurl critiques without actually having to do better themselves.