Roguelike Definition 2.0

Roguetemple presents you a small and comprehensive list of several factors for evaluating the roguelikeness of a game; those may help you get an idea of what a roguelike is:

High Value Factors
Random Environment Generation The game world and its contents are mostly procedurally generated with each game.
Permafailure (including Permadeath) The character must pay for your mistakes and choices, sometimes at the cost of his life. Restoring games is discouraged and only provided to allow continuing split games.
Turn Based Interaction All entities in the game world are queued in an endless loop and get their independant discrete turn to act.
Single command set You can access all game commands from any place into the game. There are no artificial restrictions on what actions are available in a given game situation, for example inside or outside battles.
Free form Your advancement is not enrouted into a linear progression. You get to choose what to do, how and when.
Discovery mechanics You must research or find out the nature and usages of the items into the world.
Middle Value Factors
Single player You control a single character
Plenty of content There are enough monsters types and items to make it worthwhile exploring. This is contrast of a small set of known item and monster types. (more than 24 monster and item types is a good measure)
Complex non-trivial world and object interactions Items have non-trivial usages, you can do some things which may not be obvious for the item nature.
Low Value Factors
High ramped difficulty The game gets hard very quick and you are very unlikely to win until you have acquired enough experience.
Monsters are players The nature of the monsters is similar to the player, they can have equipment, player-like stats, artificial intelligence and are subject to the same world rules
Character-based display The player interacts with the world via a user interface based on character symbols that represent UI artifacts and entities into the world.
Hack and Slash Gameplay involves around killing things to become more powerful and acquiring treasure to buy better equipment and repeat the cycle