I'm going to start off on an adventurous foot. Thanks to Ryan Vincent (Yes, I do Google any name I find, no intimidation meant) for showing me this site. My topic today is Roguelike Design from the player's eyes.

    Rogue was the first Roguelike game, for those not in the know. If you know about roguelikes, you could skip this paragraph. Rogue was basically a tile and text-based RPG that put you in control of an adventurer. You can (z)ap wands and (w)ield swords against hideous foes, and (q)uaff potions to heal yourself and (r)ead scrolls to give yourself new magical powers. Now, granted, this is not featured in every roguelike. Some, like GearHead (on whose wiki I am an admin, go to http://gearhead.chaosforge.org/wiki to read more on it) are based in Science Fiction, not fantasy, and Roguelikes can be as simple as the simple Zomband, or as complex as Dwarf Fortress (Assuming I have the names right, you can just use Google).

    Roguelikes are an unique genre. You have an ultra-simple user interface (even in ones which have migrated to graphics such as GearHead), an entire keyboard, or almost that, in controls, and an ultra-complex or deceptively simple system that runs the thing. Most use random number generators simulating dice, like ADOM, ToME, and GearHead, but some use alternate methods. Roguelikes are generally turn-based, though some such as ToME-net and others opt for a real-time interface to allow various alternate methods of play, though this is rare. Due to this, you are playing a game more like chess than DOOM (there is, however, a Doom roguelike, which I strongly recommend as an example of a deceptively simple Roguelike). There is no limitation to what a roguelike can do, many venture into 3d (GearHead, Dwarf Fortress, CastlevaniaRL, and various others). Despite their immense simulation powers, pretty much any roguelike but Dwarf Fortress (my poor 1.83 GHz prooved too feeble) can be played more or less enjoyably on any machine, due to their turn-based nature, and frequently simple graphics.

    An roguelike should have a few things to make it easy on its players:

1. An intuitive control system, or an decent inventory system with object interaction commands. Good examples are ToME, my first roguelike, and GearHead for this, because they use the controls everyone would expect. An bad example is Incursion. The Up-In-Air-Ready-To-Fall system for inventory is annoying, despite the fact that Incursion is generally awesome.
2. Character depth is one other important aspect. A character in a Roguelike is expected to have all a character in D&D should have, save roleplaying specific. He, or she, should have at least some specialties, so he doesn't feel too stereotype, unless he is. The exceptions to this being DoomRL, CastlevaniaRL, ZeldaRL, and other lighter roguelikes.
3. The ability to inspect environments is an important aspect. Even in primitive-graphics CRPG's this should be implemented. There should be a basic ability to inspect your environments, so that you can know that the floor of the crypt is covered in dried blood, or the grass is tall as opposed to short, as it helps give the player depth. Sound, however, though found in rare examples, is not part of this ability, as it does not help the player ascertain what that green comma is.
4. Help sections or tutorials. A good example of a tutorial is GearHead (1, not 2), where you start out in a town with naught but a backstory and friendly townspeople. You then get the ability to talk to Megi, the mayor, to go through tutorials, or a small introductory quest. An example of a good help system is ToME, which was easy enough for me to pick up years ago when computers were new to me. An example of a bad help system is the common ToME engine modules with a help-file referencing inexistent material. Angband is good here, for the most part, as an example of above-average performance.
5. Universal standards are useful. The main character is almost always displayed by an "@", which allows the player to know where he's at. Bad puns aside, the universal standard of displaying the first letter of an character's name, with colors and a capitalization for Greater or Unique foes, is always useful. Objects are recommended to use a non-letter character that resembles them.
6. Towns. I know traditional roguelikes have no towns, and shopkeepers are far and few between, but seriously, towns and overworlds make a roguelike much more realistic. Good examples are ADOM and ToME, average examples are Angband and CastlevaniaRL, and bad examples are NetHack and, unfortunately, Rogue.
7. Companions should be optional. Companions are used frequently in GearHead, for good reason, because the difficulty can be very high, but they can be annoying at times. The only real example of companions are GearHead, and NetHack. I don't care about the stinking pony, let me have that darn claymore!

    And that concludes this rant.