I bumped into a 645Z user that actually came from Phase One (I don't have a 645Z--wish I did) and he had no complaints. I've also spoken with a Phase One user who was contemplating switching to a 645Z.
Don't let ANYONE tell you it's not well respected.
Of course, I know there are many K3... K5... K-1 owners that couldn't care less about the 645Z as their needs are already being met.
I say, if you're happy that's all that matters. If there's something about your photos you don't like, then by all means make the switch. But my guess is if you're unhappy with your photos now you'll still be unhappy even with another make. (Think I've read that here before.
)
Edit: and by "users" I mean "name landscape photographers." The
real deal.
And, one more thing, if your photos are good, do you think anyone's going to look down on you because they came from a Pentax... especially years from now? The only people that would look down on you for using Pentax are likely people that are insecure about their own work. And they're out there, for sure. But I don't think anyone out there producing good quality photos really cares what sort of brand someone else is using; except some folks that might hang out on forums like this.