Is 1.f4 a playable opening?

playable as long as your arm and hand still work and can support the weight of the f pawn

So 1. Na3 with 100% white wins must be the best.  1. f4 is very playable, and it was my opening during my teenage years.

1. f4 is playable at any level though most masters avoid it. My personal opinion is that most losses from this opening - those that aren't due to tactics - are due to strategic errors. White's light squares will become weak if he trades off his LS bishop, which I often see beginner to intermediate players do. Then the Stonewall style position of the pawns that often arises with c3, d4, e3 and f4 become targets if you trade the DS bishop because it's a "bad" bishop... I dunno.. I used to love the opening, but I rarely play it anymore. Good luck with it

The problem with 1.f4 has traditionally been that Black can get easy equality with either 1...d5 or 1...Nf6. Carlsen demonstrated that even though the position is equal, there's plenty of room to play chess, even against the best in the world. 

Sure, it was a fast game. Sure, Black equalized. But, White found enough resources to play for the win anyway.

-0.2 and 0.0 are virtually the same to most engines.

If 1. f4 is that bad, what does that make the Dutch defense with 1. ... f5 then?  Really bad?

It's risky but that's why people play it anyway.

It would just seem that if 1. f4 d5 is dubious or poor for white (a reverse Dutch), then 1. d4 f5 must be criticized even more if one desires to be consistent in their thinking and logic.

Michael "FPawn" Aigner plays it all the time.  

1.f4 d5 isn't bad at all but 1.d4 f5 is risky and does have an iffy reputation in GM play. But for most players this doesn't really mean much.

If you don't mind playing the KIng's Gambit, you can play 1.f4. IMO 1...e5 is Black's best reply. There are some lines in the Frohm's Gambit (1.f4 e5 2.fxe5 d6) and in the King's Gambit (1.f4 e5 2.e4 exf4) which look very good for Black. So I don't like playing 1.f4 anymore. I used to play it in my late teens.

I've never played it, but its playable

Note that ANY first move by White is playable because Black hasn't moved and White can't do much worse that fall one tempo behind in trying to do proper opening goals (space, central control, tempo, force).  f4 is central enough and pointing toward f7, Black's initial weak point, to be a theoretically good move.

On the other hand, if Black plays his KB to c5 and you don't have your pieces properly coordinated, all f4 does is makes it hard to castle K-side.

That's why I like openings that get that pawn to f4 early, like the Bishop's Opening and the Vienna Game, but where I also have the option of transposing to the Giuoco Piano if Black's opening moves make f4 too risky.

From's Gambit is the worst line black can play in Bird opening. That is just "hope" chess where black gives up clear (but small) advantage in hope of white making some stupid mistake.

Of course it's playable.  Unless your universe is ruled by a super-demon who will literally prevent your hand from moving across the board once you take hold of the f-pawn. 

No but in all seriousness, I have someone in my club who plays 1. f4 regularly and it actually takes a lot of people by surprise. They don't expect it to be 'good' and so they just blunder their way through the opening. He's a very experienced player too, been playing for more than 30 years, knows all the openings you can think of and he plays 1. f4 against a lot of newer players who think they know it all.  Surprisingly most of them lose. 

Close to that: The From is one of the most fundamentally sound gambits in chess literature.

..

I do have "some" experience playing Bird opening here, and around 1300 games which turned into From's Gambit. 

So far I can tell - black is better with simple 1..Nf6 or even 1..g6.