I love ember. It is awesome. But I recently stopped using ember-cli. Here is why. Be warned this is a pretty raw stream of thought and may not be particularly well reasoned. Maybe some day I'll edit it into a proper blog post.
I get es6 modules. They are awesome and I look forward to using them one day. But right now I find them to be more of the PITA. IF I had a extremely large app I might feel different, but committing to es6 from day one has led to problems for me and my team. "How do I make this existing lib cooperate that needs to tie into ember?", "How do I debug this issue?". With globals this stuff is trivial. Open web inspector. Poke around. With es6+ ember inspector it isn't terrible, but it is not great either :/ This is has been a definite sticking point for people new to ember on our team. Hard to learn ember and battle ES6 weirdness at the same time.
Everyone keeps saying that this is for modifications to ember-cli internals, but it is quickly becoming another package manager: https://www.npmjs.org/search?q=ember-cli. Team member asked me the other day if they should use npm+browserify, bower, or the ember-cli-addon version of a library. Ugh :(.
This is mostly a personal preference, but I much prefer gulp to broccoli. Gulp streams and pipes are easier to manipulate and understand especially for our devs who are coming from previous node.js work. With gulp I don't need as many plugins, eg "grunt-" or "broccoli-" and in my experience performance has been nearly the same as broccoli.
FWIW, I actually miss ember app kit some days. It was complex, but that complexity was out in the open. I could go in and change things quite easily on a per project basis. Now it is all hidden in the depths of an NPM module. And I have a write an ember-cli addon fi I want to change things. Great another API to learn :( Before I could just manipulate the express server directly, add middleware, etc.
Bottom line is that ember-cli just isn't cutting it for us right now. Ember itself has such a steep learning curve, throwing on the additional overhead of ember-cli (and all the stuff that goes with it) has just been too much.
Don't get me wrong. I have hope. One day it might, and ember-cli is pushing hard in that direction. But we need to be productive and flexible today. That can't come at the expense of being on the leading edge or pushing the state of the art. It took me ~6 hours to reimplement a good chunk of ember-cli using gulp.js with globals. So that is what I am going to use for now.
One final disclaimer. I know lots of devs who's needs are met very we'll by ember-cli. Open source is pretty thankless work and I'm thrilled that things like ember and ember-cli exist at all. Please don't take this too negatively. All the ember and ember-cli devs are awesome and thank you for all the time you put into these tools just so I can complain about them :)
Just curious if you could elaborate on any issues you had with using ES6 modules? Can you think of anything that might help lessen that curve? I think partly the fact that the language itself is rocketing in this direction is going to help, but can you think of anything specific to the context of Ember-CLI that would have been helpful to just flat out know before hand?