If your GOG profile is accurate about your location, I'm not surprised that you hit a latency error. Blizzard games aren't particularly tolerant of high latency connections, so games between Australia and other continents have always had problems. Such games are possible, but the latency baseline starts you at a disadvantage, so both parties need a connection that is otherwise pretty good, or the initial intercontinental penalty will push you into the unplayable range. I remember playing Diablo with someone in Australia, and the latency was noticeable. I don't remember ever seeing equivalent latency playing intercontinental games with anyone other than Australians.
As for difficulty: it can be hard at first, but difficulty depends a lot on your playstyle. If you know the game's rules and how to turn them to your advantage, it can be quite easy. Some quick tips:
- If you fight in melee, have a shield. No two-handed weapon is worth losing a shield.
- A good magic item can be better than some unique items. Evaluate the bonuses of each; don't assume unique items are always the right choice.
- If you fight in melee, you should be a warrior or a rogue. Sorcerers swing too slowly. In early areas, using a sorcerer for melee is fine. Once you get to the deeper floors or higher difficulties, sorcerers should be using magic as their primary means of offense.
- If you fight with a bow, you should be a rogue. Warriors and sorcerers are terrible with bows.
- If you fight in melee or with a bow, get your dexterity up. Dexterity is critical for warriors for chance to block. Classic advice was that a warrior should put every level up point into dexterity until it maxed out, ignoring other attributes.
- Sorcerers should put points into magic unless you have a compelling reason otherwise (such as a nice item that you need more strength to wield).
- If you fight with magic, you should be a sorcerer. Warriors and rogues cast too slowly for combat spells to be worthwhile as a primary means of offense. (Utility magic, like healing, teleport, and stone curse are fine.)
- Let melee enemies come to you.
- In melee, use the right type of weapon for the monster class you face. Animals: edged-weapons (swords, daggers). Undead: blunt weapons. Demons: no preference.
- Wake as few enemies at once as possible.
- Use terrain to shape the battle. If many monsters are after you, retreat to a wall or corner to reduce the number of monsters attacking at once. If available, use a doorway to force them to face you one at a time.
- Don't chase ranged attackers into unknown territory. You'll just wake up more monsters.
- Never use any shrine without checking its effect in Jarulf's Guide. The three shrines to avoid at all costs are Fascinating, Ornate, and Sacred. Mnemonic: Find Other Shrines.
- Never use a Goat Shrine or Cauldron. These are a random shrine, so they might roll a Fascinating, Ornate, or Sacred shrine. You do not want that to happen, ever.
- Never fight in melee with a Black Death zombie. Personally, I would leave the level the moment I saw one.
If you want to see all the formulas in detail, read Jarulf's Guide. It's not a walkthrough; rather, it's a comprehensive collection of statistics, formulas, and rules.
