Diablo: The Hell 2 mod

The Hell 2 mod is a second generation mod after classic The Hell. It gives more variety (monsters, items, spells, boss monsters, unique items, item & environment colors), introduces new character classes (now there are 29 instead of 6), increases replay value and adds lots of new unique and attractive gameplay features.

What it gives you in general

1. Improved engine! Supports modern operating systems, up to win10. Play fullscreen, window, borderless, whatever, switch by Alt+Enter on the fly.
2. Fully adjustable high resoutions (up to 4K) and adjustable framerate (up to 1000 fps)!
3. Multiplayer support (it's functional, setup guide coming soon)
4. Tons of original game bugfixes!
5. MUCH more content: improved and new game mechanics, improved and new spells, more and better sorted items, color schemes for everything, new monsters, many new bosses, thousands of uniques, new and resurrected quests, improved sounds, soundtrack remastered in stereo quality and new music, etc.
6. Improved game atmosphere: even more diabolical feel to Diablo 1 than ever before!
7. New 29 classes to play (Warrior, Templar, Executioner, Summoners, Archers, Monks, Rogues, etc.) and 4 game modes (normal, hardcore, ironman and nightmare)!

Additional game info

Inventory items
Everything you equip on your character and use in inventory/belt.
Let's see what are the main differences between D1 and TH.
Item break occurs when current durability reaches 1, after that maximum durability starts depleting, when it hits 0, then the item is broken, destroyed.
Item availability depends on dungeon level and difficulty mode. All items are available (as drops) only by the time you get to play on 'doom' mode. Additionally, in singleplayer mode, item availability depends on your character's basic attributes. Which means you can't find items that are too far away from your stat range.
As in D2, Shift+Leftclick transfers potions of life/mana/holy to your belt.
Weapon switch hotkey is V.
There are stones instead of scrolls in the game now. Called relicts.
Magic books may have character level requirements.
Magic spells
There are a few types of magic damage in TH:
fire > lightning > arcane (magic) > physics > holy
Fire spells are the most diverse and powerful, holy spells deal the least damage, making undead the worst enemy types for pure casters.
Spells can be damaging, controlling or for personal usage.
Now on to spells list:
Fire bolt, charged bolt, holy bolt - standard low level damager spells. Holy bolt knocks back targets on impact.
Arcane star - damaging spell, damage is arcane, of magic type. For those who think that spell damage can be either fire or lightning. Well, now you know more.
Inferno, lightning - attack targets 20 times per second, for the duration of the spell.
Chain lightning - there is none here.
Healing - heals you, effectiveness depends on basic vitality.
Reflect - increases melee damage FROM monsters, and returns 400% of the damage back to them. Works similar to D2 Paladin skill 'Thorns'.
Fire wall, lightning wall + rings of fire/lite - not damaging spells, they are used for crowd control.
Elemental - self-targetting physical damage offensive spell. Doesn't affect undead though.
Force wave - physical crowd control spell.
Bone spirit - cuts a percentage of target current hitpoints. Can't damage undead.
Nova spells - highly damaging spells, but trigger cooldown on cast, to avoid letting mages spam these like crazy.
Fury - a spell that works differently for each class. Modifies battle stats. Gives triple shot (not to Assassins).
Fire blast - main offensive fire spell. Has splash damage (100% damage).
Ball lightning - high damage spell, has no splash.
Hydra - similar to Guardian from Diablo 1, but amount of Hydras is limited by spell level.
Golem - deals physical damage that can't be resisted by monsters. Teleports near master when gets too far.
Stone curse - makes enemies petrified and immune to all damage. Golems don't even try attack cursed monsters. Some are immune to Stone curse.
Flash - magic damage spell. Does insane damage on very high spell levels.
Mana shield - damage goes to mana 100%, but increased (as a payment). Starts at 200% on spell level 1, and decreases rapidly with spell level increase.

On hotkeys

Standard F5 - F8 are still there.
Non-adjustable TH hotkeys listed below.
I - inventory
Enter - group chat
Alt + Enter - quick switch between window mode and fullscreen
C - character sheet
Esc - main menu
Tab - map
P - pause game
F9 - F12 - adjustable quick multiplayer messages (messages can be altered in 'hellmsg.ini')
~ - display setup menu (in-game)
F1 - Fury
F2 - Healing
F3 - Reflect
F4 - Mana Shield
Q - Teleport
W - Fire Wall
E - Lightning Wall
R - Fire Nova
T - Lightning Nova
Y - Arcane Nova
U - Holy Nova
O - Town portal
A - Fiery blast
S - Lightning ball
D - Arcane Star
F - Stone Curse
G - Golem
H - Holy Bolt
J - Flash
K - Inferno
L - Lightning
X – Force Wave
B - Bone Spirit
N - Flame Ring
M - Lightning Ring
Z - Elemental
Ctrl – Hydra
V – weapon switch

Character classes

...coming soon..

On quest locations

In singleplayer, there are special locations (quest zones). They are unique, in a sense.
You cannot save game when in a quest zone. At all.
Can't cast portal there, and use stairs. Until area is cleansed (no monsters left). This is lockdown, called 'Vise'.
When lockdown is lifted, you hear the horn sound. That means you can cast portal and use stairs again.
Another feature of these zones is temporary character altering. You can receive penalties for the time of your presence on such levels. These can include life/mana regeneration, DFE, AC, attack/cast speed, resistances, accuracy, inability to cast certain spells.
I would advise against using glasscannon builds in quest zones. As your main goal there is to survive. Not die.

Links

Development blog
Official forums