I've personally never had a failure of an IGH, so can't speak to that, other than my experience has been good with them. I know some have busted their 1st and 2nd ratios on Alfines in offroad riding, particularly when they go with a lower ratio than is recommended.

The IGH's I've used haven't broken my cadence or rythm, so YMMV there. Any drive train will require a bit of a lightened pressure to shift on hills - even derailleurs. On the flats, I just shift on the fly, no worries.
I've had bikes with Nexus, two Alfines, a S3X and now a Nuvinci, and have never felt that they gave anything up in the shifting department. Of those, I'd say (and agree with you) that the shift chain mechanism was not my preference, but properly set up, it worked just fine for me.

I have nothing against regular drive trains, but find them to be less than optimal when the weather turns mucky. Since I now live in the desert, I have less of a preference - either format does just fine.