This January my group started The Slithering, and the GM allowed me to take the Gunslinger for a spin. We're currently one session in (two combat encounters), and the following is my impression after playing the Gunslinger for a bit.
So, first things first. We're playing with the free archetype variant due to being a man short (we've got a player on paternity leave), but for the purposes of my experience it didn't really factor in on the impression, as I chose "Alchemist" as my free archetype and so far I've used it for diddely squat (the one point where I could have given another player an antiplague to fight off a disease; I forgot... So he rolled his save without the added bonus.)
The Character:
5th level Hobgoblin Gunslinger
10str, 19 dex, 18 con, 14 int, 12 wisdom 10 charisma
1- Firearm Ace
2- Risky Reload
4- Running Reload
Weapon: +1 Striking Dueling Pistol
The Experience:
First off, I really liked the way the gunslinger works, that is, I like how it works with the feats I've chosen. While Firearm Ace is nice and Running Reload lets me do something while I reload, I feel like Risky Reload is necessary to stay on par with a reload weapon, even though I didn't even come close to keeping up with the other characters.
Now, the reason I say that I couldn't keep up, is because of a certain monster type which is very present in the slithering and their immunity to critical hits. On the plus side, the low AC of that gelatinous bastards also means that I never missed a Risky Reload, so I consistently fired twice per turn by starting off with strike/reload/strike as my turn one and then go into risky reload/reload/strike on the following turns.
Even though I was able to pump out shots I felt like I wasn't contributing to the team effort, which was in part due to consistently rolling at least one 1 on my d6's, but I suspect most of it was due to the crit immunity.
Max damage on a normal hit for my guy (with Ace) is 14 damage (2d6+2), but for a crit, max damage is 54 (2d10+2*2+1d10).
My one gripe after the session is that I feel like the gunslinger (or at least the gun) is a bit too reliant on critical hits. I realize I probably couldn't have picked a worse adventure to test the Gunslinger in, and overall I still enjoyed playing the character, but I felt way behind the melees in our group who while they couldn't crit either, rolled bigger dice and had more attacks.
Anyway, that was my 2p.