The RNP RF approaches is of course a biggie. It's current and enjoyable to fly.
But so is the ability to choose different engine ratings which you can't in the NGX.
The autobrake / reverse logic is far superior and works like it should which the NGX doesn't have. In fact, I'm not sure any other add-on has as well.
The NGX a/p kind of seems buggy and harsh (reported by some in the PMDG section). The iFly is much smoother and follows the magenta line much better.
Having the ACARS wx update in flight is great too. Being able to download the latest winds aloft and descent winds on the fly is a handy feature.
Plus there are plenty of options to set up according to each individual airline and their cockpit layout.
And looking over the cockpit straight ahead just looks right with the VC. Although as above, I also enjoy using the 2D panel and that doesn't seem to make it any less 'immersive'.
I guess some of us prefer something with better quality and more features. Because none of that above seems like it's lacking in any way does it?