Blake is an incredibly generic and boring character. He is essentially a Gary Stu. I would say he is one of the worst things about the movie. Think about everything you could've done with the screen time that was devoted to the incredibly boring and generic John Blake. You could have further developed Catwoman, Talia, Bane, etc.
I only recently came to the following conclusion after I went back and read some fanfics and previous posted posts on message boards prior to production on TDKR starting. I remember how many fans were trying to come up with ways on how to make Robin work in live-action and a lot of the Robin concepts fans had that I saw pop up over and over again were concepts very similar to John Blake's character - already a full grown man as opposed to a kid, being introduced as a member of the GCPD before he gets recruited by Batman, a Dick Grayson-ish personality, a character with an idealist mentality that doesn't like how the police does things and quits at the end to join Batman, someone inspired by Batman and deducing his identity, etc.
Most of the idea on how to do Robin were very similar to that and none of them came off as too interesting to me either. They all came off to me as just very generic and boring versions of Robin pitched by fans that just wanted to see Robin in the franchise regardless of how he was done. After going back and reading all that, I've realized that that is exactly what Blake feels like. He feels like a generic character pulled straight out of a not-so-professionally-written fanfic written in 2008 by a fan that really wants to see Robin in the franchise.
I also talked with someone once who told me that he believed Nolan created the John Blake character mainly because he wanted to work with JGL again and because he knew fans wanted to see Robin, he took advantage of that. I'm not sure if I can fully believe that but given what a incredible writer Nolan is, he technically would be able to create characters just for reasons like that but have them feel more natural to the story and the viewers wouldn't even notice.