One pocket is by far my favorite game...I just wish I had more time to play it.
To play the game at a high level there are so many skills that are used more often in one pocket than while playing the other basic pool games. Running balls, shot making, safety play, kicking, banking, strategy...and all of this while controlling both the object ball or multiple object balls AND the cue ball on every shot.
Now, I like 8 ball, 9 ball, 10 ball and 14:1 too, but safety play, kicking and banking are all much smaller slices of the pie in those games. Running balls is the primary skill needed in those games.
And on top of all that, it doesn't get much tougher than bunting and banking balls towards your hole for most of a game of one pocket, and then your opponent leaves you a long difficult shot at your hole that you have to fire in with a good stroke...It can be hard to pull the trigger knowing you will sell out if you miss.
I hope all of that makes at least a little sense.