Is the Blacklist a serial TV show?

The show's creator Jon Bokenkamp called it a strange hybrid of serial and procedural elements:

Each week there's a different criminal,...

... but the reason you come back to the show are the people and the secrets that they have...

Every episode usually has a "case-of-the-week" story, i.e. one criminal from the titular "blacklist" gets introduced and is dealt with. That part of the show is "procedural".

The "serial" element of the show has to do with the mysteries that the characters hold, e.g.

• Why is Reddington so fond of Elizabeth Keen?
• Who is Reddington's adversary?
• What happened to Reddington's family?
• Is Elizabeth's husband who he says he is?
• How did Elizabeth's father get to know Reddington?
• What's the deal with Mr. Fitch and the organization he works for? ...

It is a serial (rather than "episodic") TV show - there are references to previous episodes, and several on-going story arcs which have a little more revealed every few weeks.

Your question is wholly inaccurate. Every show builds character development on previous episodes. Can individual episodes be viewed without understanding character dynamics from previous episodes? That depends on the episode you are watching! Cheers, The Big Bang Theory, Friends and Seinfeld all have independent episodes but watching most "series" expect an understanding of the characters that won't always be re-explained.

To be clear, The Blacklist regularly introduces episodes with "previously," so while you may not need the pilot to understand, you need previous episodes to understand some dynamics. Regardless if you know those previous episodes, each episode does stand up individually...so far.