Padraigr - I'll be getting a K-R myself within weeks, and I've been "looking closely" at the Pentax DSLRs for over 2 years - from K-M to K-X, and now K-R.
The K-R now has the fully functional points focusing screen that the previous models didn't. It retains and inproves the very good low-light / high-ISO abilities of the K-X. The viewfinder is rated as good for entry-plus level, and the LCD/Live-View screen has been greatly improved (also the magnifying focusing function for on-tripod and macro, etc.)
Like all modern Pentaxes, it retains the ability to use the last 40-years of Film-SLR lenses, including Asahi-Pentax/Takumar, Tamron, Sigma, Carl-Zeiss/CZ, and Russian glass back into the Soviet era. Obviously the optics qualities vary a lot, but some very good lenses are available at quite modest prices.
You do need to check carefully before buying the earlier lenses - some "excellent" lenses can at first seem to have the same descriptions as "woeful" specimens... Lenses called "M42" (often good to excellent Asahi-Pentax Takumars) - need a Screw-Mount adaptor, and will be manual.
K-mount lenses, from the 1980s, but more around from the 1990s, mount directly to the camera, and can be manual, to semi-manual, to semi-auto.
There is a huge database of Pentax-compatible lenses back to the 1950s at Pentax Forum, which you can access without being a Member - but if you join, you find "Clubs" threads for everything from "most modern", to Clubs for specific lens types - M42, K-mount, Takumar, Tamron, and a lot more.
The Pentax "kit" 18-55mm is regarded as quite a good getting-started lens.
The "kit" 55-300mm is the "L" (base model, NOT like Canon's "L" lenses!) - version of the DA ED 55-300mm. The differences are that the ED is metal mount, not the L's plastic, has quick-shift which the L doesn't, and comes with a hood - which you'd need to buy for the L.
Optically the L and ED 55-300mms are identical. They are claimed to be optically the best of the to-300mm zooms available at the price. They rate higher than Sigma's popular 70-300mm DG APO lens.
The K-R does have controllable HD Video, if that's an interest. It also has the fastest Continuous shooting of the entry/entry-plus level DSLRs, at 6fps.
In additition to the usual DSLR Auto, P, A, S, M, modes, it also has a Sensitivity mode - set the ISO, and the camera does the other settings.
You can Download the KR Manual, and read it right through, which is quite informative, to see what it actually can do, and how.