The interface leaves much to be desired, but the primary functionality -- fully decentralized orderbook/exchange on the blockchain -- works great. I take advantage of the low liquidity that everyone complains about by leaving low bids and high asks on the book. They often get filled, at least partially, at considerably better price than more liquid exchanges.
I can also rest easy at night knowing that my funds are safe and can be retrieved from the smart contract into my public address anytime I want. They are making a good deal in fees, so hopefully they improve the UI a bit, though. It's definitely not noob-proof.... I'll say that much.