For me, it depends on how long the wait actually is. One or two years is pretty standard but the six year wait between George R.R. Martin’s A Feast for Crows and A Dance with Dragons would definitely have put a damper on my excitement level. Luckily, I quit that series after the third book—not because it wasn’t good, just a little too wordy for my tastes. I’d fall seriously behind on my reviews if I were reading 1,000+ page novels regularly!
I find that it’s easier to get excited about an upcoming release when you remember how the previous book ended. The longer the gap between installments, the fuzzier my memory gets. I’m not a big re-reader, so I really appreciate it when authors include a 1-2 chapter recap at the beginning of each novel. Although admittedly, I was a little frustrated when I heard that Karen Marie Moning pushed back Burned‘s publication date. Fortunately, it was still months away so I hadn’t really begun to get overly excited for it yet. Now, if she would have done so one month before the scheduled release that would have been a different story! Kinda like what Kalayna Price did with Grave Visions last summer. It was within my sights and then BAM—pushed back by a whole year! My interest in that title has indeed diminished a great deal as a result.
All this to say, that long waits between installments doesn’t mean less interest as long as the publication date doesn’t get pushed back too many times. After the second or third reschedule, I begin to question if the author has lost their writing muse, and what the cause of the delay is. I understand that shit happens but publishers shouldn’t announce release dates until they are pretty sure that they will be able to deliver on-time. Once it’s on their website for the world to see, they’ve made a commitment to their readers and should try to honor it as best as they can.