I run long term, detailed sandbox campaign games.
Low power, very political, heavy social interaction.

And while being good at it may be subjective and biased, my games do last and go on with no abating.

Judging myself is a bit tough. Not sure about how good I am, but here are the campaigns I am comfortable running:

1) Ravenloft: Just very familiar with the setting and ran it so much in the 90s and 2000s that I feel I know it like the back of my hand. One of the few published settings I have this level of confidence wit.

2) Horror: Comfortable with most kinds of horror campaigns

3) Intrigue and investigations: I like to have lots of prep time for these (more so for investigations) but feel very much at ease running them.

4) Modern Settings: Very comfortable running games where the pcs are criminals or law enforcemet agents of some kind. Would include counter terrorism here as well

5) Historical: Like number three, I need more prep time for this but am comfortable doing the research and running stuff set in the past.

6) Fantasy Campaigns: quite comfortable doing any standard D&D style campaign

7) Asian fantasy settings: run stuff like oriental adventures plenty of times. Prefer wuxia these days but did a pretty epic fuedal Japan campaign before.

Middle Eastern fantasy campaign: Pretty comfortable in this kind of setting. Though my overconfidence on this one led to the biggest bomb of a campign, ever. I think I learned my lesson though.

I run many different things so I feel confident with almost any genre. According to the feedback of my players over the years my best games are:

- Horror. I am good at creating a creepy ambience, disturbing NPCs and horrid situations. Also, I kill PCs and don't give a fuck about it.
- Vampire. People like the depth of the intrigue and social backstabbing, how each NPC has distinctive quirks and backgrounds ready to be discovered and used, and how every action has consequences and Humanity is always at the front.
- Gritty and grotty fantasy, or historical fantasy, or historical. Probably for the same reasons that horror and Vampire together. People has liked a lot my S&S games, my RQ Vikings games and my Aquelarre games.

Generally speaking, I am at my best running tough games, in unforgiving settings.

I'm best at CT MgT T4 Traveller and d6 Star Wars with systems and the campaigns that they produce. Most of my campaigns play out the way a Larry Niven or Robert Heinlein novel reads and the way a Cowboy Bebop or Planetes anime goes.

Dark & heavily political fantasy. Not stereotypically grimdark, but a few shades lighter.

My strengths are "comedy" and "conspiracy mindfuck".

I can't manage horror or straight historical to save my life.

Gritty, hard SF with lots of political intrigue. My games aren't "hard-boiled" so much as seared: burned to a crisp on the surface, but still raw and bloody in the middle.

Gritty fantasy horror and cinematic hard sci-fi. Or, at least, that's my guess, as these are the types of campaigns where I've consistently had the best reactions from my players.

Over the top, Earth shattering epic fantasy.  "Not only do your characters matter, but if they fail it's disaster".  Go big or go home.  
Heroic post apocalypse, with more focus on making things better for others than just survival.