For larger F# projects you will probably use a bunch of .net libraries. It is of course an advantage of F# that you can, but it also makes the language feel like an uneasy hybrid. For example F# functions are called with a different syntax than .net functions/methods. Haskell feels much more consistent.

I prefer F# for larger projects because it makes a bunch of pragmatic compromises. IMHO languages which a singular vision (Scheme, Smalltalk, Haskell) are great for learning and expanding your mind, but when it comes to larger real-world projects, dogmatism just gets in the way.