Relative to a 1.08 experience, the most important source of power is not knowledge of the classes and skills so much as the changes in the game itself.
Assuming you knew 1.08 with the LOD expansion, you know of runes and charms. High level runes were "The Runes of Never-Find". Here they are (almost) common.
Charms were a trade-off between 40 cells of space in your inventory and gained resists or gained damage power. Here, with 99 spaces, and *rare* charms, you can do both.
Rune Words were powerful, but you had to find a *white lable* item to get Larzuk to socket it, or find a grey-label item with the right number of sockets. Here, you can take any rare weapon, armor, helm, shield, *belt*, that you like, cube it with PGems = 2*the number of sockets that you want, and the item now has the number of sockets that you want. Now put in the runes for the rune word you want. Yes, in the Rare item! Find *the* *perfect* necro shield ("voodoo handbag"), with +2 skills, resists, and +3 to Summon Resists, Revive, and Lower Resists, and Rhyme it! Find *the* *perfect* necro wand, with +2 skills, Mana, Life, and +3 to bone spear, Corpse Explosion, and Golem Mastery, and White it.
There were class-specific items, Now there are about three times as many, including necro-specific armor. Find a rare one with skills and resists and Smoke it. Find a rare circlet with +skills, mana and life, and Lore it.
Relative to 1.08 these items would be "Ith" hacks. Here they are items of moderate power. The monsters you face are far tougher and more numerous than in 1.08.
In 1.08 you had unique items. Here you trip over them. The more common uniques here are little more than "good" rare items. Some are truly the substance of delight. In 1.08 you wondered where to farm for the unique that you wanted. Here the answer is simple: Gheed. You'll find body parts and oils and potions that sell to Gheed for very large sums of gold. Gamble items you want until you get what you want.
With all this joy comes some changes we don't love. In the jail, or catecombs, you might encounter King Leoric and his troupe of magic-arrow minions. This can be a 1-hit-kill on any character not yet out of act 1. Plus he and Andariel swap places randomly
You might also meet The Butcher, another 1-hit kill on any character under level 50.
In the jails, they're both behind "hidden" walls, so dont'
unless you're ready for the (loss of) experience. There are other "surprises". Without them, we'd go play Mario and kick turtles. You'll get addicted like the rest of us.