I've only seen the 1st four movies and found all of them interesting, but only really love one of them; Jackie Brown.
For the most part, while I find them facinating, they are also just plain hard to watch. The violence and sociopathy are gut wrenching and yes, there's little to empathize with.
So, what's facinating? The interactions of wildly original, over the top sociopathic characters. Being aquainted with a few sociopaths in real life, sometimes I wonder what would happen if Kristin were to interact with Gia ... well that's what a Tarrantino movie is; seeing that played out on the screen. There's a certain amount of satisfaction in that. Except many Tarrintino characters are smarter and more interesting than Kristin & Gia, so the dialog is memorable.
And there are the odd horrific, can't-take-your-eyes-off-them characters; GoGo, TheGimp, Beatrix.
But, have you seen Jackie Brown? It's one of my top 10 all time favorite movies. If you have and aren't impressed, let me know and I'll elaborate. If you haven't, see it and let me know what you think.