We are fully aware of etherdelta weaknesses.
But this is the problem with all fully decentralised trading platform, user experienced is very poor.
The same problem is with https://variabl.io/. You can trade there CFD on Ether but maturity is 24h ! Quite funny, like binary options. My trading experience is rather poor but they still work on final version.
From the technical point of view, there are important features that a good decentralized trading platform should have in my opinion:
(1) blockchain architecture to offer high throughput and secure transaction processing,
(2) security, traceability and auditability of transactions (encryption of transaction data and decryption for audit),
(3) a fast and flexible matching engine,
(4) solid protocol for clearing (margin management) and settlement transactions,
(5) market design for promoting liquidity,
(6) fast and responsive trading user interface to support a large number of simultaneous connections,
(7) platform design should be ledger agnostic (Bitcoin, Dash).
From the client point of view the most important factors are:
(1) Friendly and responsive user interface,
(2) Liquidity,
(3) Security.
By the way, do you know Metatrader 4 ? Probably the most user friendly trading platform ever produced.