Sigh, there truly is no franchise the entertainment industry won't keep dragging out until it finally shits all over whatever legacy it has. It's like developers and/or production companies can never let something end on a high note, they have to keep milking it and will only end something on a sequel that's a forced, hated installment that's a blatant money grab. The only place you see any sort of artistic integrity in that regard anymore seems to be, funnily enough, in television. For all the crap shows out there, the truly good ones seem to know when and how to end triumphantly and lower the curtain. Well-received, well-done programs like Farscape, The Invisible Man, Monk, to name a few have known when its time to come to some kind of final resolution. But tell that to the games industry with its continual sequels for series like Halo, Final Fantasy, Zelda, Resident Evil, and so on.
Now, I'm not against sequels on principle. When they're well done, I enjoy following the continuing adventures of likeable, interesting protagonists. But when they start feeling like a plodding, neverending series of hackneyed and trite installments to an idea that's become stale and forced, its clearly time to yank the plug.