I really like my K5 for the handling, size and prime lenses. The handling is great, especially the way all the control buttons are easy for the right hand fingers to find, and the utility of the famous "green button" in manual. Image stabilization is in-camera so any lens is automatically stabilized.
You can set up a good kit with essential lenses a lot cheaper than for Nikon or Canon, but you probably will have to shop second hand and/or ebay for some of them. For longer or specialized lenses, you may have to buy from Asia. I have had no problems finding the lenses I wanted, over time. (Forget about finding a great super-tele lens, even a 300mm f/2.8 is extremely rare.
I feel the autofocus quality isn't as good as Nikon or Canon when it comes to darker situations, or for action sports where you need fast autofocus and focus locking.
I like my full-frame limited lenses because they are fast and quite small (and have Leica-like build quality), but they are forced to live on a crop-frame camera. So my 31mm is a 46mm equivalent and my 77m is 105mm equiv. That isn't so bad, but my 35mm equiv is an out-of-print 20mm or 24mm. I chose the 20mm FA for the wider angle, but I think the 24mm FA* would be a slightly better choice.