Agile is great in theory and if you can get everyone involved to understand it then it's great in practice, too. The reason I say agile is a failing concept is because those of us in the industry understand it but are remarkably terrible at selling it to the non-technical people we need to have involved in order for our projects to be successful. What good Agile methodology really drives at is an effective amount of involvement from all parties -- customer, analyst, technical team, testers, operations, etc. Most businesses want to fire things at their IT department and then go off and do other things while the project is underway. This is clearly more conducive to the "waterfall" model (which we all know is terrible) and it prevents them from ever seeing and effective agile development implementation.
So, yes, Agile is a failing concept. Not because the idea bad, but because it's so incredibly difficult to implement fully, and it's not very valuable when partially implemented (you basically just turn it into mini-waterfalls).
I foresee DevOps ending up with a similar problem.