I feel they are going the wrong direction with the Turtles. They are going loud…and they shouldn't have.
If I was going to re-imagine the Turtles for a gritty style. I would look at modern Ninja, martial arts films and start building my lore there.
I would focus on the idea that the Foot clan ARE Ninjas, and the theft and violence is never seen. Nobody knows what this organization is…and that is crippling the city in fear. It sounds like the first movie…but don't make it about recruiting our kids. The Foot Clan doesn't care about kids or even stolen goods…it cares about control with fear. And as the city starts to panic people start doing stupid things. Bringing the city further into chaos.
That is how I would handle Turtles….then you make Shedder not a robot but some badass Ninja, that almost seems mystical in skill. Play off of the idea that people believe Ninjas have sort of "magical" powers….Ninja tricks. The movie should focus a lot on deception and no mercy…and of course revenge. The Shedders downfall is his blind rage for Splinter, and you need to really play that up.
For the Turtles, big and bulky doesn't work. I think lean, silent…brutally efficient.
Basically, Michael Bay had a chance to make the Turtles into something modern and special for adults but just made another transformers loud movie.