Let me illustrate how they failed with the example of the .aero TLD. When I want to visit the website of British Airways, one of the largest airlines in the world, I typically Google for "ba". The first search result is britisharways.com, not britishairways.aero. Now you can repeat the same experiment with all the other major or minor airlines, and the top search result always will be a .com (or a ccTLD) domain.
This how you can tell .aero has failed; it's main target users are simply not using it.
If you already have your .com then you don't need new TLDs. But .aero may come in handy the next time someone wants to start a new airline (which is admittedly pretty rare, so .aero in particular was probably a dumb idea).
I think the succesful gTLDs will be the ones that appear commonly in trademarks like photo, pizza, sports, mart, lube, etc. It may become much more common for the domain to be the primary trademark, even for businesses that aren't particularly internet related. Fredspizza.com would be a confusing name for a restaurant but Freds.pizza less so.
> But .aero may come in handy the next time someone wants to start a new airline
The problem is that ICANN has already set it up so that if you have the trademark on "flying.com" that nobody can get "flying.aero" (well they can, but you can take it off them easily). So why would you even bother with the .aero domain unless you own the .com too?
If ICANN goes by trademark law, then you should be able to register something generic like friendly.aero without infringing on friendly.shoestore. If they don't then they are being stupid. If there are going to be hundreds of TLDs, you can't automatically protect every trademark in every TLD. Trademarks are not supposed to work like that.
I don't understand the situation well enough to say if it is a "money grab" or not, but it seems like another good reason to abolish intellectual property.
Doesn't sound like a failure at all; you navigate using Google. I would assume this is typically where their traffic comes from. With that being the case it might as well not have a TLD at all; it's all but invisible to the user. The domain could very well have been .aero and you still would have navigated to it successfully. Isn't that all that matters?
Ok here's another example: easyJet, one of the largest budget airlines in Europe, paints easyJet.com on the sides of their airplanes, not easyJet.aero, as you can see on this photo:
This how you can tell .aero has failed; it's main target users are simply not using it.