Why do I like the Denon 103r so much?

My observations regarding dl103R and classical are consistent with Schubert's comment. Does other forms of music equally well also. My search for the perfect cart for me ended with the DL103R. I recommend building a vinyl rig around it for anyone seeking vinyl magic and near perfection on a budget. There are good reasons for it being around for as long as it has apparently. A true gem!

If really on a budget, which many good folk are, the DL-110 is not all that far behind.

It's also possible that the cart just clicks with your arm better than the Shelter. Arm-cart compatibility is a big thing, just as speaker-room compatibility. When you find a pair of speakers that just work in your room, it's like a revelation. Sounds like you might have something like that going on. Enjoy and don't screw with it too much!

I have only used a Denon 103pro. Undoubtedly it had the most unadulterated tone and timbre I have heard.

I was using a VDH retipped Crown Jewel (aka Shelter 501) when I got my first 103R - and much preferred the Denon for its involvement and superior tone and texture and presence.
With this cartridge I find myself appreciating the music itself and how its being played - rather than the hifi qualities.
That said, the SoundSmith retip can greatly improve the top end (especially) and clarity in general. Focus, separation, recovery of ambiance and other soundstage dimension/details are also much improved. The stock 103R is a very good tracker, but the line contact retip tracking is significantly better. The musical qualities of the stock cartridge are essentially retained, though of course it does sound different.