I'm very much a pragmatic kind of person, and my unpopular opinion about code is that Lisp is the greatest single language ever designed, if your goal in designing a language is to produce articles proclaiming it as such.
And I am sooo sympathetic to the promises Lispers make. I want to believe. But ultimately, show me the code. Why are the stellar Lisp success stories so few and far between that one of the big ones is Paul Graham's from the 90s?
If it's so powerful that almost no one can use it, and it rules in almost no problem domains, ... how is it so powerful again?
Lisp's popularity came too early. Lisp really needed some relatively powerful machines to take advantage of it, and when it was actually popular most machines were way too weak for it. Now that machines are finally powerful enough to handle it, it's no longer popular, and it has no army of programmers using it as they are using some of the more popular languages like Java or Javascript.
So, yeah, you're unlikely to see that many "killer apps" made with it, as the killer apps of today usually require a lot of programming resources that the Lisp community just doesn't have. What apps Lisp programmers do come up with are mostly not going to be so uniquely Lispish that they couldn't be replicated in another language (see Reddit's rewrite from Lisp to Python[1]).
On the other hand, there's Emacs. That's one killer app whose power arguably hasn't been beaten or replicated elsewhere. But that very much depends on your taste -- and if you agree with that you're probably already a Lisp convert.
Then there's the whole "worse is better" thing. All sorts of inferior technologies have triumphed in the marketplace -- for reasons that usually have little to do with their technical merits. Lisp has itself been a victim of that. It's a vastly superior language to so many more popular ones out there (and many other language designers agree, if the regularity with which Lisp features are pilfered in to other languages is anything to go on), and yet so many programmers are really ignorant of it or have only been exposed to little toy Lisps in their college years, mistakenly thinking that modern Lisps are no better, don't realize how much their own favorite languages owe to Lisp, nor how much more that their language doesn't have that Lisp has to offer.
Don't confuse lisp-as-an-executable-device-to-think-meta and lisp-as-one-of-programming-language-choices. Alan is talking the former.
The idea---not just to think about programs per se, but to think about abstract properties and operations of certain category of programs and to be able to actually write it down---gave the exponential power to you. Lisp was the first such tool as a programming language that allowed you to break the ceiling of first-order thinking.
Nowadays there are other languages that provide meta-level tools. And once you get the idea, the language doesn't really matter; you can apply it to any language, albeit you may have to build scaffolds around it to compensate lack of language support (Cf. Greenspun's tenth rule). So, if you already got the idea through other languages, it's good for you. You'll see Lisp as an arcane prototype of modern languages.
But note: since Lisp can write meta-level description in the same language as the base language, you can top up this ladder infinitely, meaning you can think of program-generating-program, then program-generating-program-generating-program, and so on, using a single set of tools. It is indeed powerful but somewhat crude, so modern advanced languages intentionally restrict that aspect and just try to cover the sweet spot. Even if you're familiar with metaprogramming, it may still be worth to play with Lisp to see what (meta)*programming is like, to know its pros and cons, and to get the idea that might come handy someday when single-level metaprogramming isn't enough.
I'm very much a pragmatic kind of person, and my unpopular opinion about code is that Lisp is the greatest single language ever designed, if your goal in designing a language is to produce articles proclaiming it as such.
And I am sooo sympathetic to the promises Lispers make. I want to believe. But ultimately, show me the code. Why are the stellar Lisp success stories so few and far between that one of the big ones is Paul Graham's from the 90s?
If it's so powerful that almost no one can use it, and it rules in almost no problem domains, ... how is it so powerful again?