Yes, to some extent there were debates about how the implementation would work, but also about how they would interact with all the various other features of Java, most of which were not constructed with lambdas in mind: generics, exceptions, inheritance, and so on, not to mention lots of fights over the syntax.

For instance, there was a long battle over whether () would be enough to invoke a lambda, or whether some sort of apply() or invoke() or .() method would be required, and a lot of the problems with () come down to differences between the way fields and methods are inherited in Java, esp. w.r.t. shadowing. I don't even know how it all came down, but it gets nasty, a lot of this stuff just wasn't designed with lambdas in mind.