I'm still really enjoying this book. I can understand the complaints that the last two arcs haven't had enough closure, but I really like the fact that PAD's setting up all this stuff(the Tracer, alternate reality uncle Ben, Ms. Arrow, Quention Beck) for an epic storyline down the road. You don't see spidey writers doing this kind of planning beforehand these days. Plus, I think these both of these arcs had plenty of content, and also worked well by themselves. Just my opinion, though.
As for PAD leaving, I wouldn't worry about it. He's wanted this gig for ages, and he's the kind of guy who sticks to his projects. Unless the book gets canned(VERY unlikely), or an editor with a grudge kicks him out(somewhat unlikely until JoeQ's running marvel, since he's always been very supportive of PAD), I'd say he's staying on the book at least until issue 50.