This page attempts to give answers to some of the questions that keep coming up among SLEX players.
Q: What's up with this huge amount of playable roles and races? I can't be bothered to learn what all of them do!
A: You can always just play a dwarvish valkyrie or other combo that you know from vanilla. Playtesting the new roles and races is more fun of course, but the choice really is up to the player.
Q: What are "hybrid races" and why does the game keep asking me whether I want to use them?
A: Essentially, it allows your character to be of several races at once. All the eligible hybrid races have significant impact on how the game plays, so they can actually be considered "special modes". However, for e.g. determining whether a corpse counts as cannibalism when you eat it, your main race is the only one that is considered.
Q: Help! What does item X do?
A: Get familiar with in-game item descriptions. Open your inventory with i and then select the corresponding letter of an item to see its description. This will display several pages of information telling you stuff about the item. If the item's base type is not identified, it will say "Unfortunately you don't know more about it. You will learn more if you identify this item.", in which case the full information will be hidden until the item is identified.
Q: Why doesn't SLEX have feature X from Nethack 3.6?
A: Because it's based on SLASH'EM and therefore ultimately the 3.4 line of Nethack. I consider 3.6 and onward to be beyond terrible; every once in a blue moon it adds something that is actually good, in which case I cherry-pick the feature in question for inclusion in SLEX, but most of 3.6's gameplay changes are utterly repulsive to me. Don't expect me to implement that stuff.
Q: Why doesn't feature X work like it does in Unnethack (or dnethack or <insert variant name here>)?
A: Because SLEX isn't Unnethack, duh :P And it's not dnethack or any other variant either. When I steal features from other variants, I reserve the right to make changes to them so as to ensure they actually fit into the general theme of SLEX.
Q: Why are some of the items in my inventory prefixed with * or ! glyphs?
A: These are reminders that the item is made of certain materials. * and ^ are glass and obsidian, respectively; these items will break if thrown or dropped from a height. And ! means the item is made of ether, which contaminates you by being in inventory; actually equipping such an item contaminates you faster. It's also possible to turn on the "materialglyph" option that will show a prefix for every item material, to make it easier to tell at a glance what material an item is made of.
Q: What is this "contamination" thing and how do I fix it/what happens if I don't fix it?
A: Contamination can come from monster attacks, traps, items made of ether, being in the gamma caves branch and more; get contaminated enough and your wisdom will be reduced over time, with an instadeath if it goes below 3. It can be cured by successfully praying on a coaligned altar, reading a noncursed scroll of remove curse or zapping the wand of remove curse; amnesia can also help in a pinch but has negative side effects. Chatting to a nurse may offer a service that lets you cure the contamination too.