My only real complaint with Heroku is that once you grow out of a basic no frills app, prices really rack up. For example I was looking to move an app I'm currently developing on a VPS to Heroku, but I use a ~200MB Redis database and just that will set me back $110/month.
Heroku is great if you can fit your app within the free tier and great if you're happy to spend a few hundred bucks a month, but in between those two I'm often better off with on or two $20/month 1GB VPS.
I feel exactly the same. I do a few hobby sites and I can't use heroku for this reason. People often reply that it's not meant for hobby sites, but I'll always bet on bottom up technologies, and cutting out hobby sites is not bottom up.
Heroku is great if you can fit your app within the free tier and great if you're happy to spend a few hundred bucks a month, but in between those two I'm often better off with on or two $20/month 1GB VPS.