I thought that was another cracker myself. Bill and Nardole continue to get consistently better characterisation than we seen from companions for a long time and the episode took an interesting concept and delivered it well without falling foul of too many Moffat-isms.
As for the questions of "why'd everybody kill themselves" I personally think that whilst it could have benefited from more of an exploration, I don't think the episode unravels as a result of this. We don't actually know the exact detail of what is in the Veritas yet - it may have revealed more to the reader than just "you're not really real and this is all a simulation", although I'd wager that this alone would still be sufficient information for many people to top themselves. What if it reveals the purpose of the simulation, and the fact that it's being used to plan an invasion of the real Earth - many would take their lives as they would see it as a way of hindering the aliens research into their weaknesses.
Similarly on understanding that you are in a finite simulation, one that has a clear goal and therefore a potentially short lifespan, might make you more inclined to take your life. Moggy you talk about why does this reality mean any less than the "real" one - well in the real world most people have the expectation that they are contributing to life in a manner that will outlive them, through all sorts of ways such as children, accomplishments, provision for future generations, generally doing their bit to make tomorrow better than yesterday for some subset of the world. If you know you're in a simulation which could be turned off at any point, or re-calibrated or adjusted in some way that de-values your efforts to date, well that is a very different prospect, and every reason to not want to continue for many people.
Something they could have included might have been that not necessarily everyone kills themselves on hearing the truth and that would explain why they're are genuine crazies in the world who go around spouting that nothing is real!
Either way I loved it - funny, entertaining, thought provoking (to a degree expected of this kind of thing), and with the requisite amount of scary stuff to keep the kids behind the sofa.