Different slide designs have unique ways of using gravity to accelerate children downward in a forward motion while sitting down on something slick, at their most basic definition. However, kids don't normally use slides or other playground equipment solely in the manner intended. They do whatever they want to, walking or running up slides, going down headfirst, and other things that could end up with a potential slip or fall impact injury. Generally, it's a good idea to extend the safety zone at the based of the slide from the minimum 6' measurement. Add the difference beteen the highest and lowest point where a child would be seated to the 6' distance, and this typically provides a better safety zone area in which children are likely to impact as they exit the slide. Again, that's just if they use it as intended.
Another thing to consider is what type of slide, based on the age of the children and their specific needs. As an example, it's not a good idea to have a slide with any form of bump in it for very young toddlers. They tend to slide a little quicker, can go a little airborne when they hit that bump, and statistically land on their face or head. Not a good experience for those under age six, and often the circular covered plastic slides are a very good option, because they can't go over the side as they go down. For younger ones, it's also beneficial to have handrails on anything that changes elevation, like slanted steps instead of a vertical ladder. They can lack upper body and hand strength needed until age 6, so their little hands get sweaty and they lose their grip, resulting in a fall.
Many people might be surprised to learn that 58% of all playground fatalities are due to strangulation, and many of these have occurred on playground slides. The problem is anything protruding near the top of the slide on which some article of clothing or something worn around the neck could get caught when a child gets ready to slide down. They slide, something catches, like a young cub scout's canteen strap and they become strangled, dangling on the slide surface. It's horrific, and it happens too frequently (because it shouldn't happen at all).
Age appropriate equipment is required to maintain proper safety, and obviously we wouldn't expect an 18-month old toddler to handle a playground climbing apparatus, nor would some simple colorful tires embedded and barely extending above the ground be of interest to a 10-year-old. Post the age range for each playground, so people can be properly informed, and maybe create separate play areas within the same playground for different ages. There are different abilities, and slides are an important part of any playground.
Similar to swings, it is normal for the safety surfacing at the base of the slide will get the more wear than other playground areas, and it's also where a pad is recommended for loose-fill surfaces, so it isn't displaced so much that the geotextile fabric separating the surfacing from the sub-base becomes damaged. Those rocks may migrate inside the safety surfacing, which isn't good or safe to land upon, plus it can also affect the drainage system, and having to remove the surfacing to repair this is costly and frustrating.
If it's a public playground, it is a a good idea to use a very heavy molded kick pad at the base of the slide, something heavy that stays in place, and is hard for anyone to easily remove and steal. If it's a residential playground, you could just use an anti-fatigue mat, which runs a fraction of the cost of one of the much heavier public playground kick pads. Those with the slanted edges and squared open space honeycomb underneath them, that squish when you stand on them, are perfect for this. The underside interlocks well with the rubber mulch pieces, placing them about halfway within a 6" depth, so there's 3" of rubber mulch beneath the pad, and 3" above it. This helps it to stay in place best, while still providing 3" of depth beneath the pad for fall impact protection off the end of the slide, while protecting the drainage system sub-base and geotextile fabric.