Optogenetics is an incredible tool for probing and dissecting the activity of neurons within neural circuits. It’s gives enormous power to scientists to perform more causal manipulations and test ideas more concretely than observation or genetic manipulations alone. I’m not sure why it would be considered a toy, though the utility depends on what you do with it. So far this has been primarily limited to understanding the brain but there’s work to develop clinical therapies using optogenetics as well. I collaborated with Karl extensively in my PhD work with some others in the comments here. It’s exciting to see his work get this recognition.

There's a new strategy for treating loss of photoreceptors in the retina: reprogram fibroblasts with optogenetics to turn them into new photoreceptors. NEJM just had an article on this.

it's a great tool for molecular elucidations. there's still a big gray area as to the interpretation of some results in the context of terms such as "memory" or various feelings, but the optogenetics framework is undoubtedly the most impressive interface to the brain ever created