Or Hell difficulty for that matter...
Is it me or are the other difficulties like completely unplayable? Like cant get out of the first room unplayable? Like takes 40+hits to kill a level1 skeleton unplayable? Whats the point?

Seems insane to even bother with it.

I do like the expansion though, thats cool

The higher difficulties are only playable if your character has high enough stats and good enough equipment.

you can actually start in level 1 in nightmare difficulty and still beat the game. its really not that hard but you need a little luck
as for hell you need to be at least level 10 to beat that difficulty.
i have done the 2 above with the warrior.

In multiplayer, entering Nightmare required character level 20. Entering Hell difficulty required character level 30. Higher difficulties are very playable with those levels.

THanks that makes more sense

As previously been stated, Nightmare and Hell difficulties are meant for higher level characters.

In fact, the original game did not have any difficulties beyond Normal in single player (but there was a trick...), it was only added for the Hellfire expansion. Diablo Multiplayer always had Nightmare and Hell difficulties, but they required a character to have reached level 20 or 30.

Now about the trick, if you have a high enough level multiplayer character you can create a Nightmare or Hell difficulty, leave, then create a new singleplayer game, which would now have that difficulty.

Unfortunately NM and Hell doesn't actually bring that much more to the game, and the game's item generation is bugged causing item drops to have magic prefix/suffixes as if it had dropped on normal mode. So you're better off just doing hell runs (dungeon levels 13-16) on Normal than moving onto Nightmare and Hell (with the exception for if you plan to level your character to 50, in which case moving onto the later difficulties is eventually required).

There is one more reason. The Helm of Sprits - one of the rarer items in the game, can only drop on the first few levels of Nightmare.

Beware that the difficulty is not saved, so this trick must be repeated each time you restart the program.The game's bugs are extensively documented, and this is the first time I've ever seen someone claim that this particular aspect of item generation is a bug. Could you explain why you think this is a bug? The base items are upgraded as a function of the modified mlvl. The qlvl remains tied to the unmodified mlvl.

Maybe it's not a bug, maybe it's just overlooked. Either way, it means item drops in early Nightmare and Hell are more or less useless to a character high enough level to venture there.

Overlooked by whom? Jarulf's Guide notes that this happens, and this effect is why you can get certain rare unique items only in higher difficulty games.

Phree is incorrect. Higher difficulty settings result in an increased chance for higher quality item drops.

Overlooked by the developers. And it wouldn't be the only case of nonsensical item logic in the game (the bow Deadly Hunter for example has a +200% damage vs demons property which only functions on Melee weapons)

The quality of the base item increases, the quality of affixes do not. So while a Long War Bow may drop in Nightmare Church, its prefix and/or suffix will be no better than had it dropped on normal.