We liked the older Pentax K-7 a lot, and our only significant criticism was its relatively poor high ISO performance. The new K-5 brings all the things that we liked about the K-7 - the compact, solid body, and generally well thought-out ergonomics, and excellent feature set - but adds substantially better image quality, in both still and movie modes, and a host of other improvements. In our opinion this makes it one of the best APS-C DSLRs currently on the market.
Image quality is now up there with the best of its competition, and all of the K-5's key systems are reliable and effective. Throw really nice ergonomics into the mixture and you have a compelling little camera that we have really enjoyed using.