well I am sorry that your writing and grammar are below standard but mostly I am sorry that most everyone who responded was such a douche and so high and mighty to understand what you were asking. I understood what you were posting about but maybe it is because I am not stuck in heaven with all the other perfect people on this thread who have never made any mistakes or maybe it is because I am not a douche bag who thinks it is so important to spell everything correctly and have perfect punctuation in an online forum.
Now to answer your question. Diablo is such a good game because it is a simple hack and slash with a deep grinding and item collection system with a very wide verity of weapons and other items. The pacing in both the Diablo games is perfect for their length. The character classes cover the perfect range of variety for a hack in slash with the second game expanding the range to cover a better selection of differing skills and play styles then the three from the first. The dark storyline touches on aspects of life that people find intriguing because of the way they play into most people's everyday lived but in a fantastic way by touching on commonly known archetypes(ie. the fallibility of faith and religion, the fall from grace that shows even the most noble of people can be corrupted and fall to a darker way of living, and the struggle against what seems to be unstoppable odds, ect...) The is a lot of filler to be found in the game that strikes at the gamers imagination and has them craving for more.
The second game expands this with so many aspects, the ever changing look of your character, the better and more fantastic effects that you get from abilities and magic, The ability to play with the same character through multiple difficulty settings and even the ability to truly test your skill by playing an unforgiving game where once you die there is no restart button.
Diablo 3 is highly anticipated and I assume that it will drain many hours from many people