For me, 2 spring to mind.
Defying Gravity … it just hooked me and a shame it never continued. I remember one thing jumping out as a great future tech which has almost come to pass being the characters transferring money between each other by just touching their devices to each other.
The other is Whitechapel the detective drama. It needed 1 more season to close out , and the creators said they could have done it with a special 2 episode story … but alas it’s never happened.