But I easily know one when I see one.
These are roguelikes:
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http://i1.ytimg.com/vi/yReGKEBvCqQ/maxresdefault.jpg
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How DARE you slander Cataclysm in such a fashion! (kidding)
But honestly, I don't consider Cataclysm (or my fork DDA) to be roguelikes. The lack of overarching quests/goals*, low emphasis on "dungeons"** and overall tone seem to me to be more than sufficient to disqualify it. How does it stack up against the more thoughtful definitions:
Intent
It fails at this one, I have no intent to keep the game roguelike, "Any resemblance to a genre, living or dead, is purely coincidental."
A roguelike derives interesting gameplay from the interplay between permadeath and procedural generation...that's my pet definition.
Some might disagree that it meets the "interesting" part (ouch), otherwise meets it.
Privately, I use the "is it like Rogue?" test. It`s maybe crude, but I like the simplicity of it. It also helps a lot because nowadays it s very much in-demand to be considered a roguelike. Sometimes bit too much perhaps.
So if it`s turn-based, has permadeath and random content generation - plus some sort of a quest - it`s a roguelike. For me Next step down would be a roguelikelike for those more daring experiments that stray from the above formula and then "an X with roguelike elements" for assorted gatecrashers.
Disqualified by the "plus a quest" part. Would definitely qualify as a "survival RPG with roguelike elements".
In the old days the definition of RL used to be something like "An RPG game with poor graphics (compared to mainstream games), but much more complex mechanics and richer content".
It meets this one... maybe? Is an overarching quest implied by "RPG"? Definitely emphasizes content and mechanics over graphics.
akeley's definition is closest to my sense of what makes a roguelike, though I'm admittedly warped by the 'bands, so my internal definition is probably more properly called "'bandlike" than "roguelike"
If I see too advanced graphics, it just makes me think "I wish that effort were put in the gameplay instead". Almost total focus on the programming aspects of the game design is a huge part of the appeal of roguelikes for me.
There's some validity to this, particularly if only one person is working on the game, but I prefer to focus on wanting deeper mechanics than disproving of graphics. I don't know if someone could pull of a good-graphics hardcore roguelike, but I don't want to discourage them from trying. For my part, I'm simply bad at graphics, so it's a non-issue.
I have even been thinking lately about making a completely text based game.
Interactive fiction roguelike? That would be amazing if you could pull it off. I've been thinking about working IF elements into a roguelike, specifically procedurally generated room/item/monster descriptions.
* To me, having a goal, the game being "winnable" is a critical criteria, DDA doesn't have a win condition.
** Dungeon-type exploration seems fairly core to me, though this one is admittedly more shaky.
*** Permadeath, or at least "Permaconsequences" is on the list. Good point about X-com.
**** Procedural generation gives me pause, because I want to say "that's an implementation detail", but what it really means is that you aren't playing the same "levels" over and over as in "traditional" games. So in that case yes it's critical.
***** This is a "footnote-like" aside.