I can't believe how overlooked this series is. The combat looks amazing and the art in it is easy on the eyes. Can anyone fan recommend a good entry title or even just the best one in the series?

I've only played Summon Night: Swordcraft Story, but I loved every bit of it (even the primitive parts) and I would definitely recommend it.
 
In fact, I loved it enough to blindly buy the Japanese language novel-sequel, though I haven't gotten around to actually reading it yet.