> > Would, say, a Ruby or node.js-oriented web developer find the F#/.NET community lacking, incomplete, unfriendly, uncool? Is there even a community to speak of?
> The answer in my opinion is yes. This may change, given recent efforts by Microsoft, however evolution will be slow because the whole ecosystem has to change, not just Microsoft.
A suspicion gnaws at me. I try to rid myself of it but alas, it holds fast and unyielding. That suspicion being: you know very little about the F# community. What statements you make, they seem descendents of generalizations from your experience with the .Net community. Happily, F# is not like the stereotypical .NET community (I must be so specific, in order that I not offend the subset to whom your claims do not apply). There is a strong culture of embracing open tools and code; Microsoft is not looked at for direction beyond what basic support they provide.
The community is neither lacking nor is it unfriendly. It is small, yes. Uncool? Opposite of! But opinions run with tastes. Incomplete is a tricky matter. Certainly it's not going to have as many libraries as Python or the JVM, but neither is it some kind of backwater.
There are excellent build tools like FAKE and paket. Awesome ideas like—why, take a look at how fantastic the HTML type provider is, and it works in real life too! Most of the time =) [http://fsharp.github.io/FSharp.Data/library/HtmlProvider.htm...]
There are tons of cool libraries available, most of them open source, with generous licensing terms. Stuff with Haskell heritage like fparsec, fscheck, the blazing fspickler combinators (serializer) or more computation oriented tools that let you target and run on the GPU or Here: Automatic Differentiation (after which, loss minimizing Machine Learning algorithms are made much easier) [http://gbaydin.github.io/DiffSharp/]. Or the DataFrames library: http://bluemountaincapital.github.io/Deedle/
Type providers also allow easy use of UI builders. Web frameworks and also, js targeting can be reached here: http://fsharp.org/guides/web/. You can target Unity3D and apparently, also the Unreal Engine.
There are interesting projects looking at distributed computation (https://github.com/fsprojects/Cricket and ilk) or light weight concurrency, in Hopac's take on the Pi Calculus.
F# was one of the earlier languages with light weight threads, a solid async story and first class events (pre-reactive trend). Active Patterns (not unique to F# but more common in) take us close to Predicate Dispatch (http://c2.com/cgi/wiki?PredicateDispatching). There is much more I could list and hopefully, I have piqued some interest.
But it's not perfect. Adding Functor support would be very useful. A while ago, in an early Active Patterns paper, there were hints that generalized algebraic datatypes might soon be introduced. Nothing came of that. Higher kindedness is nice but not as much missed—it is my suspicion that, the gains from each level of types that can be parameterized over, quickly saturates.
There are lots of cool projects going on in F#, and while, as a language it's definitely not as powerful as say Scala or Haskell; the tools, libraries and environment, alternate ideas as well as breezy syntax, do make up. Having used them all, I wouldn't say it is any less expressive, it just...prioritizes differently beyond the core functional ideas (REPL, sum/product types, currying, closures, point free application where possible, Hindley Milner inference, immutability by default, pattern matching and deconstruction, etc., etc.).
It strikes a lot of middle ground across many planes, in terms of pragmatism vs functional purity—that is its ML heritage (but perhaps even more so, bargained in exchange for the .NET ecosystem). Most functional languages focus on types in terms of algebra, F# does too but only basically, instead it focuses more on the easy bridging of types with unruly data.