What's so great about it?
It has a very engaging story. It is very open world, allowing you to pursue that story in whatever direction you choose. The world is fully interactive. All objects can be dragged and dropped, moved, stacked. Some areas are only accessible if you take crates and stack them to build your own staircase.
The npcs have a daily routine. They sleep at night, get up and spend some time around the house before heading off to work. If you want to break into the bank, then you would have to sneak into the banker's home at night, kill them and take the key.
However your party members have their own sense of morality and will complain or leave you if you commit crimes in their sight (theft, murder). Your party members are AI controlled in combat, so that you don't have to micro manage them. You can set their behavior style: attack nearest, attack weakest, attack strongest, run away, etc..
There's a huge number of sub quests that are plots in of themselves. Almost never does it involve anything like deliver this to so and so, or bring me 8 foozles.
Just keep in mind, the game is nearly 20 years old so some thing considered standard in rpgs will not be found in this game. For one, there is no journal for your quests. It's up to you to keep track of what you are doing.
The game also requires you to eat to avoid starving to death. And so you have to carry food along with your items and gold. However even gold has a weight/size. It's a physical object in your inventory like anything else. And since things have a size, you may have your carry capacity showing as 24/40, but when you try and drop a plate mail chest piece into your pack, it will say "Won't fit" instead of "Too Heavy". In that case you have the option of taking your shield out of your left hand, and carrying the armor in your hand instead.
If a character dies (and you don't have the one npc in your party who can res) you have to carry their body and equipment to the king, who will heal or res for you. That involves a great deal of inventory juggling to get all their equipment to fit on the rest of your party, and to get one person's carry weight down low enough to be able to carry the body.
But they eliminate the packrat mentality in this game because shopkeepers sell, they don't buy. So there's no reason to keep pieces of armor or weapons you have no intention of using. The only reason in the early game is if you have not yet filled out your party (8 max) by meeting and inviting the various people who will join, you may want to store some equipment for those later joiners. The only items you can sell for gold coins are gems (to the jeweler), gold nuggets and gold bars (to the mint), and silver serpent venom (to the apothecary).
The entire world is persistent. You can leave anything, anywhere and it will stay there. Containers don't reset.
Also inventory is a container and not a list. Open your pack and you see the little graphical representations of what you are carrying piled up in the container. Your in game map, is a map in your inventory you click. The same thing for a sextant to locate coordinates, or a watch to check the time.
The amount of detail in the game that is just a 29 mb download for the main game and 3 expansions is amazing. You can travel by walking. By a horse and carriage you buy. By ship you buy. By magic carpet you find. And these things are full sized, not just little icons your party disappears inside. You can also use magic to mark a location (on one of 8 magic stones) then later cast recall on one of those stones, to return to where you were when you marked it.