Gambhir is under-appreciated so his bitterness is understandable. Somewhere between all the adulation for Tendulkar, Sehwag, Dhoni, Yuvraj, Zaheer, his contribution for Indian cricket is often undervalued.
Between 2007-2011, he was the best all-format opener in the world and played match-defining knocks in two World Cup finals. He does not get the amount of respect that he should.
Perhaps his rapid, premature decline played a big role. He was done by 2012-13 which should have been his prime years, and the likes of Rohit and Dhawan stepped up immediately after his retirement which made people forget about him rather quickly.