I must say I'm growing more and more fond of the Slider idea... The thing is, back in L2, I usually hated this skill, because more often than not, it ended up backfiring, by turning a lemming into a state where he couldn't be saved anymore, because he would always turn around at the wrong places and thereby lock himself out of a level. There is one Egyptian level in particular where IchoTolot explicitly mentioned this in his Let's Play (saying "so we just don't make him a Slider").
While drawbacks make a skill interesting, of course, this is also something that might make people hesitant to actually assign a Slider to a lemming - if it is a permanent skill like in L2, at least. In that case, people would probably go with a Floater or Glider first before trying a Slider, if either of the former are available in a given level.
However, thinking of the Slider more as a downward Climber than a surrogate Floater instead, this would open up many new interesting interactions, especially with the Jumper, now that jumping-off a wall seems to be just as agreed-upon as jumping towards a wall.- You could have drops which are deadly, but because there are no Floaters, Gliders, or Stoners, and the wall on the side the lemming is coming from doesn't have a straight edge, you actually need to jump across a gap to the other side in order to give the lemming a wall to hold on to so that he can slide down safely.
- You could have straight walls where a lemming can slide down and then, before he actually reaches the ground, jumps off into some tunnel in a wall on the other side.
Both of these seem particularly fitting now that WillLem has created the Lara Croft sprites precisely according to my instructions! The Slider being a permanent skill would still be an interesting option, of course, enforcing turning-around consistently. Just like being a Climber can be a drawback if it causes a lemming to go over a wall and die in a place where every other normal lemming would simply turn around on said wall, being a Slider and looking in the wrong direction compared to everybody can still result in interesting puzzles.
It just seems like L2 in particular had a hard time creating such good puzzles, so that the Slider often ended up in a state where it was so risky to use that the better advice was simply to not use it at all.
But as said before, the Slider would not be the only skill whose potential was extremely wasted by L2. Even the Laser Blaster, as limited as it might seem in its application, still has a wider range of use (like the aforementioned "dent the ceiling to cut off the Shimmier" example) than L2 manages to explore successfully.