I used to be very obsessive about finishing anything I'd started, but I've gotten better. (Still not perfect, but better.) And yes, knowing I'm not committed to the end has made me more inclined to take a risk on something new.
I don't need earth-bound, but I do prefer human, even if just metaphorically human. Deep ideas, complex worlds and strange species may make for interesting settings, but unless the author makes it matter to me then all the rest is worthless.
I mostly read genre fiction* (or straight-out non-fiction) but my definition of acceptable science-fiction and fantasy (for example) is more selective these days than it used to be. I suspect it's a bit like many people will be with romance, you learn the particular variation you prefer and that's what you keep your eye out for. I am willing to give most things a try, but books outside my normal comfort zone will generally need the spur of some extra recommendation - just like I can get on MR, and especially here in the NLBC!
But I still come back to the idea that there are some things my brain just isn't wired to appreciate, and it would probably take drastic amounts of education to change it. Finally recognising that is about when I worked out it was okay to stop reading a book before the end.
* Some of what I've read recently has hit some curious genre confusion. For example some of Ellen Klages' books are published by TOR.com, known for their science fiction. As a result her books get categorised as sci-fi even when they're not. Passing Strange is small-part fantasy, part-romance, part historical ficton. And something like Wakulla Springs (Andy Duncan & Ellen Klages) ... I'm not really sure what you call it, but certainly not sci-fi.