What preferable additional functionalities should a great e-commerce website be offering its customers?

A Great e-commerce website should offer to all customers:

a. Good Visual Quality.

b. Easy to navigate.(Translated in Other language in case of geographical presence)

c. Easy to land on e-commerce Page, or Contact us Page.

d. Product and Service visually highlighted.

e. FAQ;s and Terms and Conditions well written for better customer satisfactions. 

f. Mobile and IOS platform user friendly,( in case customer is navigating on Phone)

d. Well designed for re-marketing (In case of returning Customers)

- Multi payment methods

- Easy checkout

- Easy tracking system for order shipping

- Caching the website (CSS/JS/HTML/Images)  to be easy browsing itand check the website speed on all devices.

- Daily or weekly newsletter with the latest offers- SMS with coupons

- Auto voice call to confirm orders - Multi shipping channels

- Live support & Email support.- Good design team.

- Non hidden fees

- Faq, about us, terms, privacy policy ... etc,

You probably didn't launch your e-commerce site to sell your products only to customers living in your country. Your site is on the world wide web, so I hope that you're planning to leverage this platform and sell to customers across the globe.

If you are (and you should be), you should think of adding the following:

• Multi-lingual support (10 languages will cover95% of the world's population)
• Address format sensitivity (ask your customers for their address in their format, not yours)
• Multi-currency (customers prefer to see prices in their own currency)
• Customs duties and tax calculation (customers need to know EXACTLY how much your products will cost them, in the end. Besides, nobody likes surprizes at the time of delivery)
• Affordable shipping rates (would you pay $40 to ship a $80 t-shirt?)
• Multiple payment methods (not everyone has a Visa, MasterCard or American Express)
• Easy returns policy (unless you sell bespoke products, think about offering a 'no questions asked' refund policy)

All of these are abandonment milestones, where customers get frustrated, nervous or discouraged while on your site. Addressing these will dramatically drive your conversions up.

Every e-commerce company is now concentrating on how to make better filters and how to reduce abandoned carts number.

Also make sure all your designs are responsive and work perfectly on all devices and screens.