The big difference here is that when Rails came out it solved a real problem. Every other popular web technology at the time was much, much harder to use and slower to develop in. Since then it's acquired some inevitable complexity but most of that was in response to somebody's need for a feature. Merb will accumulate the same complexity if it's successful.
To me this just sounds like Common Lisp vs Scheme all over again.
The fact that there is a full-stack version available doesn't mitigate the fact that the multitudes of custom stacks out there are going to mean two bad things:
1. The default full stack will be a lot less thoroughly documented, tested and debugged because a lot fewer people are using it.
2. The chances that I can just jump in and start hacking productively on somebody else's Merb app are slim because it's likely I'm not familiar with some of the components you're using.
I still don't understand at all why I'd want to use Merb. What problem are you trying to solve here? Being slightly better than Rails in a few respects isn't even close to good enough to compensate for the lack of documentation, code maturity, available programming expertise, public success stories etc that Rails has going for it.
I just don't get the appeal of Merb at all. Rails was such a relief after a few years of roll-your-own--web-stack Java. Why would I want to go back to dealing with all the little incompatibilities and bugs that creep in once you start mixing and matching pieces to build your own stack?
I don't see how that follows at all. If the biggest issues with Ruby are performance and memory management how does changing the language spec help fix that? If anything a stable language spec should help nail down the bugs in the engine.
It would be nice to see some progress made on the interpreter but I think it's to Ruby's credit that the language design hasn't changed that much in the last several years. A lot of the activity on the Python side has been fixing things that weren't well thought through in the first place.
You're right that Rails expects you to take the whole stack and doesn't offer you choice. DHH and I consider that to be a huge advantage but it also means that Rails won't be a good fit for every project.
That said, I don't see anything in Merb that would tempt me away from Rails for new projects.
You're never going to love every decision made by the designers of any platform. The thing is, you're likely to make just as many missteps on your own. Every once in a while it's worth it to start with a clean slate but I don't think Rails is even close to that point yet.
I don't get it. One of the best things about Rails is that I don't have to pick and choose my components. I use what everybody else is using and I know that means it's likely to work and be reasonably well documented. Any small gains I might achieve by swapping out one layer of Rails are going to be more than offset by the extra complexity of my unique Merb environment.
DHH's arguments about "opinionated" software seem to have been lost on the Merb crowd.
Is a great console music player.