The K-5 was good, but it did suffer tungsten low-light and fast lens focus issues, which were resolved to my satisfaction in the K-5II/s.
Ergonomics and great sensor (and value for money) make the K-5II a classic for me. That's why I have two of them
. I'm able to take great landscapes and make really decent prints of 75 cm (30"), sometimes even hand-held or with a monopod, something I wasn't able to do with previous cameras. Subsequent cameras, even the K-1, haven't been compelling enough (for me) to move away from the K-5II. You could say the K-5II hit my sweetspot of value for money, ergonomics, dynamic range, function and output, which I suppose makes it a classic. But I will look at the Pentax APS-C K-3II successor as a possible replacement.