It's an interesting first generation entry into the storage market. And it's pretty.
There is tremendous benefit to the grid in being able to absorb demand spikes in the battery and sheilding those from the grid. That also releives the ratepayers of paying for additional generation to meet those demand spikes.
There's an opportunity in the markets that will exist, to arbitrage power when the grid needs it. I think there's an additional benefit of providing an alternative to net metering for solar owners in an uncertain policy environment where there are continual attacks on net metering policies.
I think Tesla has missed a couple opportunities - 1) only having DC in is great for solar systems, but if you want to grid tie your battery, you will need to buy another inverter. 2) only having AC out limits the potential efficiency of a system that could stay DC (to power lights, electronics, motors, etc...) from the solar generation to the consumption with no inverter losses. 3) Increasing intelligence in the battery to actively manage demand would be another great DR resource that could be sold to the utility along with volt/var optimization capabilities.
I think those missed opportunities are true from the information I could gleen off of the website. But it's limited information - if someone has more info, would love to hear it.