Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
If there's one thing I've learned from past experience, it's that Slackware fans are a loyal group. To say anything disparaging about their leader is to risk their internet wrath. That's not to say that *all* Slackware users are blind fan-boys; that sub-group just happens to be the most vocal.
Slackware, like Debian, has a very large and long-lived user base who are quite happy with their choice in distribution. I see these two as lumbering beasts in the Linux landscape: stable but slow to change, with more agile distros dancing about at their feet. I've never been much of an elephant person.
One thing that Slackware has over Debian is a single leader, Patrick Volkerding, who has complete control over what goes in and what doesn't. To the best of my knowledge there is no Slackware "committee" or any Slackware "social contract." What Patrick says, goes.
The upside to this is that Slackware releases are generally very regular and have very few surprises. The downside to this is that you may or may not agree with Patrick's decisions, and if you don't you're just out of luck.
Slackware is perhaps the closest thing on the market right now to a "generic" Linux distribution.