I have purchased many times from Flipkart and I have had pleasant experience most of the time. The only time I felt not so good was when I ordered redmi 1s and it took more than a week to deliver even being a flipkart first customers.
Also their Billion Day sale was a big disappointment. If they want to fight with global e-commerce giant like Amazon they should ensure that their website can handle the traffic with out throwing up 404 error often. I hope they learn from their mistakes and improve on all the aspects.