Honestly that's not far off. Bebop and Rocksteady are scene stealers. Even when they are human.
As for Casey... pretty much everything about him is wrong so go in with low expectations for him and Shredder.
Awesome. I've had five movies with the Turtles, April, and Splinter, and more than half of that had Shredder, too. Krang, Bebop, Rocksteady, and the Technodrome are the draw here. I mean, I might be into it anyway -- I didn't hate the first one -- but those four are literally what I'm interested in seeing realized on the big screen.
I have no expectations for Shredder except that I actually kinda liked Iron Shredder and this one looks like weaker sauce. But as noted above, don't care much.
Casey fits into the "more than half the movies" bit, too (which is an odd metric, seeing as there was an odd number prior to this). But between that, the 2003 cartoon, the 2012 cartoon, and the IDW comic, I was already disappointed when we didn't see a return to the Clint Eastwood-like psycho of the original cartoon.