King's Gambit


that will not always be the case. there is no guaranteed win for any opening. And as your skills progress in chess, so will those of your opponents.
the opening is not the magic cure all. there's a lot of water between the opening and checkmate, a draw, or resignation.
IMHO, these are some of the reasons to consider when choosing an opening.
a) do like playing it?
b) do you understand the positions that it leads to?
c) do you have confidence in it? meaning you would play it against anyone, win, lose, or draw.
d) does it provide a workload of theory that you have the time and ability to process?
example: for me, if I played the Kings Gambit as white, the only reason would be because I would not have to face every single other 1.e4,e5 defense. no Petrov, no Phillidor, no Ruy Lopez, no Vienna games. etc. I could concentrate on one game and whether it is accepted or declined. good luck👍

I don't play it or face it in my openings, 1.e4 I never play e5 as black, as white I never play f4 as a second move. To unfamiliar to me.

This is just one example of the King's Gambit: the King's Gambit Accepted, Knight's Gambit.
Black could also decline the gambit by 2....d5 or 2.... Bc5.
Likewise, even after accepting, White has a few other options: 3. Bc4; d4; Nc3 come to mind, though generally only Bc4 is likely to be seen.

Underrated? So people think it's even worse than it actually is?

'It loses by force' - Fischer
Fischer has said more insane things than this one, but not many.

The King's Gambit....
https://www.chess.com/blog/RussBell/the-kings-gambit
or you can check out the Vienna Gambit, which is considered to be an improved version of the King's Gambit.....as explained here....
Introduction To The Vienna Game & Gambit...
https://www.chess.com/blog/RussBell/introduction-to-the-vienna-game-gambit

'It loses by force' - Fischer
check out the citations relevant to Bobby Fischer's famous quote asserting that the King's Gambit is busted in the section - Defending Against the King's Gambit - towards the end of the article....
https://www.chess.com/blog/RussBell/the-kings-gambit
EDIT: Check my reply below to @tygxc, regarding the Chessbase article on the King's Gambit being an April Fools prank. I have also corrected my blog article content related to this particular issue.

Apparently Kramnik was not aware of the conclusion of the Chessbase article I cited.....i.e.,
"...In fact we found that 3.Be2! is the only move that avoids a white loss."
Of course this was in reference to two supercomputers playing each other....
Busting the King's Gambit - This Time For Sure!....https://en.chessbase.com/post/rajlich-busting-the-king-s-gambit-this-time-for-sure
EDIT: Check my reply below to @tygxc, regarding this Chessbase article on the King's Gambit being an April Fools prank. I have also corrected my blog article content related to this particular issue.

@14
That was an April 1 fool's joke, look at the date of the article.
@tygxc -
In fact, I just now finished doing some additional internet research on that article, and discovered that you are correct - the entire Chessbase article about the King's Gambit being busted was an April Fools joke/prank perpetrated entirely by Chessbase with the complicity of the person, Vasik Rajlich, who (falsely) claimed in the article to have conducted the computer analysis corroborating the bust.
Apparently (and I was not aware of any of this until just now), Chessbase had, for years, made a tradition of pulling these kinds of April Fool's pranks. Here are a couple of Chessbase articles revealing that the King's Gambit article (ref my post #14 above) was, in fact, an April Fools prank...
https://en.chessbase.com/post/april-fool-it-was-the-trump-problem#discuss
https://en.chessbase.com/post/the-chebase-april-fool-s-prank

In fact the Chessbase 'confession' article implies that the 3. Be2 move was included as one of the subtle clues that readers should or would pick up on that the article was an April Fools prank. That is, it is supposed to be apparent that 3. Be2 is either not a particularly useful move or that it should lead to a draw. On the other hand it would be interesting to know why Tartakower chose to play that move in his game against Bogoljubov (New York 1924).

The aforementioned King's Gambit game, Tartakower-Bogoljubov (New York 1924), is annotated in the superb tournament games collection book "New York 1924" by Alexander Alekhine (Russell Enterprises, 21st Century Edition). where Alekhine, after analyzing its pro's and con's, concludes his evaluation of the move 3.Be2 as follows...
"...this backward maneuver of the bishop is not to be recommended, for the reason that it carries with it not the shadow of a threat, and it allows Black, in addition to the temporary pawn plus, the choice between several worthwhile developing plans."