Well, I think a case could be made that a card game like solitaire is the real original roguelike/roguelite/roguelike-like, etc.
Procedural generation, indeed. heh heh

Not exactly. Peaceful just makes gone with all the creepy critters. They aren't allowed to spawn at all.

Unless you save in a softlock.

One situation that can come up, in a procedurally generated game where keys work like in Zelda (each small key can be used once, but the key isn't tied to a specific door):
Two locked doors, A and B.
Before the doors, there is exactly one key that can be found.
Behind door A is another key, as well as a required item.
Behind door B is nothing of note.

This situation is certainly solvable, but if you use the first key to open door B, it no longer is; by simply using the key the "wrong" way (and there's no indication which way is correct), you have been softlocked, and if you save afterwords, you can no longer beat the game from that save.

(Incidentally, I believe at least one bug in the Zelda 3 randomizer (since fixed) could lead to this sort of situation.)

Wasn't there a similar situation in the actual release version of the game? I might be thinking of Link's Awakening.

Important it is. It would feel as pointless, and as a false promise, to invest time in a long doomed run. I just don't like playing against loaded dice. It's also why I don't like long RPGs where you can realise at the end of the game that your build had no chance of success (typically, the skill points in diplomacy, barter, stealth, swimming, waiting, painting, smelling and nail clipping turning out useless in a last sequence that absolutely necessitates maxed-out swordfighting and translating).

The basic contract is, for me, "try to complete this game : you can if you play well". Streams of good/bad luck may play a role along the way, but if the deadend is determined from the start, I'd like to be told. Else, I see it as some breach of that contract. Like a hidden "your side isn't allowed check my king" clause at a chess game.

I don't mind pre-scripted "bad endings", though, when they still are the game's completion. They actually tend to be quite awesome (but it's hard to extrapolate without spoiling some favorite games here).

Well, you've got this.

(Also, that made me smirk.)

I think there might be a dungeon you can't clear 100% if you use a key in the wrong place, but you can still get the dungeon item and kill the boss.

In Link's Awakening, I believe level 8 might have had this sort of issue. Also, level 3 (called Key Cavern, incidentally) actually contains an extra key, found in the room right before the boss, to prevent this sort of issue from arising.

(Note that, from Zelda 3 onward, small keys are associated with the dungeon in which they are found, and can't be used anywhere else; this is not the case in Zelda 1 or 2. Then again Zelda 1 actually allows you to *buy* keys.)

Would you have the same issues if the games were short (like, say, a complete playthrough being a half hour or less)?

Yes, it is important. It is not OK, if player loses a game (in basically any genre) because of sheer random, without any chance.

Ideally, there should be a risk/reward system in place, that is the toughter is the "seed" the harder is to solve and win the situation game put you in, the greater the reward (in terms of points, rare tropheys, maybe even some secret info about lore). However, it is not an easy task, so majority of games that rely on randomness can be forgiven for not implementing this thing.

Not as much. That's why I specified "long", realising there are cases of impossible short runs that don't bother me much. Solitaire card games are an exemple. The goal is to explore whether you've been dealt a win combination or a lose one.

But still, it's a matter of degrees. I prefer Freecell to Solitaire because success in Freecell depends on me (there's only a couple of unwinnable card deals in the immensity available). A short unwinnable game is still a bit of a flaw, to me. Like a labyrinth generator failing to build an exit (or a roguelike that walls some stairs out, with no possible devices allowing to reach it). If I get an impossible situation in a short game's random map (say, in some "Into the Breach"-like or "Desktop Dungeon"-like), I just go "oh well", and restart, with the vague impression that it hasn't been thought through thoroughly enough by the devs. But I prefer having faith in the fact that any presented puzzle is solvable and therefore is actually a puzzle.

It's also a matter of announcing it clearly. A "mate in 4 moves" exercise would annoy me if the answer is "you can't, lol". But if the question is "can you ?", then why not trying to find out the answer. But this has to be the purpose. And most games (with unsolvable seeds) explicitely demand "do it" instead.

I also make an arbitrary difference between unsolvable seeds determined at the start of a long game, and an unsolvable situation determined by some randomozation at a later point. FTL can throw me into a deadend situation, okay. If that deadend situation is pre-determined from the start, it irks me much more. Mathematically, there's not much difference between both situations (and the difference is invisible anyway), but cognitively it changes everything to me.

Although interesting, having an unsolvable seed just sounds like a trendy gimmick that a developer would implement for the sake of Kotaku articles...

I spent a few minutes trying to ponder if it could ever be enjoyable. It just sounds like a gag - and if I were to play a game in which victory were impossible... well, I would stop playing that game.

I'm probably gonna get downvoted for my ignorance here but here it goes.

I actually thought "rolling" an unlucky seed was par for the course for roguelikes. I was interested in picking up FTL but after watching totalbiscuits WTF is video on the game, I started thinking roguelikes were a waste of time where you're at the mercy of RNG.

There was a part where TB died and when he continued the game, an unbeatable enemy appeared in front of him and TB knew he was going to get horribly screwed. He died again but the way he reacted seemed like it was normal for things like this to happen in roguelikes. While watching the video, I couldn't help but wonder how people could recommend FTL when there's an RNG element which will set you back. Because of this, I haven't bothing picking up FTL regardless of the amount of praise it gets. Losing progress to RNG isn't fun.

"The luck based mission" is one of the video game tropes I hate the most. For me, RNG really hurt Crimsonland (lower tier weapons shouldn't be spawning late game), it rendered the latter parts of Jagged Alliance 2: Unfinished Business unplayable. It was annoying in Lord of the Realm 1 (when farming grain). I'm sure there's more but those where the 3 that got under my skin teh most.

But I don't really understand roguelikes so there's a good chance I'm wrong but the insolvable seed possibility is one that really turns me off roguelikes.

I think it is not ok if seeds are not solvable, it is one thing if I can't win a Level because I made an mistake, but if I can't win a level because of an ERROR in the level generation that makes the Level unbeatnable, that it is a BUG in the system that has to be fixed.