I think the biggest feature is that you get (up to) linearizable consistency while still being FAST, meaning you can rest assured that any writes are actually permanent, even if a server or two fails (assuming your replication factor is set appropriately).

It's not FoundationDB per se that makes this special. It's the ability to throw out hardware RAID and remove a layer of Expensive Things That Go Wrong At The Worst Possible Moment.

Once you've got replication handled in the right place, the only thing dedicated RAID hardware is really giving you is hot-swap capability (which, yeah, you do still need).