It's playable and enjoyable without spoilers.
As for winnable, that depends what you mean by spoilers. Information about monsters is observed and recorded during encounters, and passed on to future characters using the same savefile. Most people wouldn't consider these spoilers, but they're very useful.
To survive in the deeper parts of the dungeon (below DL40-50 or so) needs a bit of knowledge about the game's mechanics (for instance, how much damage is taken off a breath attack that you resist), but all of that information is included in the faq/help files. Not really spoilers, but you wouldn't want or need to dig through it until you get a character to that kind of depth.
There are some depths in the dungeon at which monsters that can paralyse you, or confuse or blind you, etc. become frequent, or at which dragons that can breathe for more than your max HP start appearing - below those depths one needs to either have the relevant resistances, or be really cautious. What those depths are might be considered a spoiler, though they were in the (somewhat outdated) Angband Newbie Guide so YMMV. If you see a dangerous monster, the monster memory will tell you what depth it appears at, so it's possible to work out all of those depths for oneself. Using monster detection magic obsessively makes all of those depths irrelevant.
Finally, the extent of Morgoth's powers and the quality of equipment you'd need to beat him would probably be a spoiler. But if you can get to DL99 and beat Sauron, you can probably survive a quick reconnaissance mission.
TL;DR - yes
Dauntingness compared to Nethack: don't know. The numbers get bigger by the end, but there are far fewer arbitrary rules to learn.
