I'm a professional photo retoucher, and I depend on display calibration and profiling as well as printer profiling for certified color proofs. We also have to maintain a working environment that complies with all color recommendations. Having said that, display calibration for gaming and entertainment purposes is completely unnecesary. Not only you will not see improvements (the before after image is riduculous), but in gaming, from RGB (developer) to RGB (gamer), there's no color management. In fact, after calibration, the results could even be the oposite of that before after image, as sometimes, full gamut isn't used if a small theoretical profile like sRGB is targeted. If the developer was creating games with real life color swatches or measured LAB values, only then display calibration would be necessary.