No GUI Installer
While it's technically true that the Slackware installer is command line text, it doesn't usually require typing long lines of cryptic text. It uses either query-response or Dialog widgets -- I forget which -- that are no different functionally from GUI message boxes, radiolists, and checklists. What is more daunting perhaps is the lack of an apt-get style automated installer with conflict resolution. Finding Slackbuilds for software not included in the distribution can be a drag. And installing non-mainstream software -- especially stuff that doesn't install with ./configure, make, make install can be tedious
OTOH, if you need to solve some problem and you search for a generic Unix "How do I ...?" or "How does Unix ...?" solution, Odds are that the solution you find will work cleanly with Slackware