For me, it starts and ends with the people: Andy, Gordon, Helen, Patrick, the Nevilles, the Reuss', George Guerrero, Matt Murphy, Tim Tyler, Pam Brunton, Tony Cicarello, all but one of the other dealers I have dealt with . . . without exception wonderful to deal with, nice, friendly, accessible, helpful.
In addition to the great cast of characters, there is the history of innovation. K&C, which started as just one of many glossy 54mm manufacturers of victorian era miniatures, through both design and accident, created the hobby we enjoy today. They launched the larger (60 to 65mm) matt, WWII and modern war hobby. They were the first company to push sculpting and painting quality of toy soldiers towards that of very expensive military miniatures. Interestingly, companies like First Legion and Tommy Gunn seem to be trying to take the quality from where K&C has presently pushed it, even further towards the Russian Military miniatures, basically copying Andy's idea . . . something the First Legion fans sometimes overlook.
In the mid-1990's they launched the high quality (and highly expensive) vehicle, aircraft and diorama industry we see mirrored today by companies like Honour Bound Gold Edition, First Legion, Figarti, Hudson & Allen, and TW Terrain. Then in the late 1990's they produced the affordable polystone vehicles and aircraft which led so many new collectors into the hobby. Andy has truly been one of the great innovators of our hobby.
Oh yeah, and there are these really cool books chronicalling K&C that make collecting it even more fun and interesting . . .
Finally, I am a big fan of affordability, reliability and resale value. K&C has been there for more than 25 years, and its production schedule has become as reliable as a person could hope for. Many many immitators have come and gone over the years, but K&C remains. Additionally, the resale value of K&C items reflects the consistent growth of the K&C collector base over the years. Despite the fact that prices have gone up quite a bit over the past 4-5 years, K&C is still the most affordable option for the matt collector. If you want to build a substantial collection of good quality matt figures and vehicles, K&C remains the best option.