The Diablo series has its definite charm. It is influenced by Castle of the Winds, a very, very old game. And Castle of the Winds is influenced by Rogue, an even older game from the 80s. And yes, I played both of those old games religiously and beat them many times. You were a little icon moving around a maze fighting monsters and getting treasures and exp, learning spells and skills. It was great.
The first Diablo took this concept and made it fancy. And it was awesome. Sure, its hack-and-slash, but its also tactical, in what spells you develop first and in which ways you kill your enemies, or certain combos you find effective. The story is not bad, either. It is actually pretty good, especially in Diablo II. The various class abilities are great as well. The game is not as dimensional as D&D-esque games like Baldur's Gate and Icewind Dale, but that is the point of Diablo, to eliminate all those dimensions and create a well-refined game about killing demons and developing your character through various spell trees. To this effect, I think its a great game series in its simplicity and story.
However, in terms of a quality RPG computer game, it is no where near the likes of the Baldur's Gate series, Icewind Dale, Arcanum, Planescape: Torment, and all of those Black Isle games. Those are brilliant CRPGs. How can I forget Fallout, too. These games are so dimensional that you can take almost 100 different paths to finish the game. The story stays the same, and the results, but getting there can be much different, depending on your race, alignment, class, etc. And I love how a sorcerer can learn non-sorcerer skills sometimes. Diablo doesn't even begin to approach the sort of dimensions that these games have. And these games are not always hack-and-slash. They are quite strategic, actually. Battles are real-time, but you can pause them, and think carefully about your next move before it happens. You can talk to various people in the towns and learn different things. They are innovative, deep games. I recommend them to anyone interested in role-playing and fantasy.
I am looking forward more to the next installment of one of these games than anything else. Neverwinter Nights was all right, but it still wasn't as good as those games listed above. The graphics interface was terrible, and the dimensionality was actually surprisingly limited. I didn't care for the story, either. It seemed like it was trying to be a D&D-based game, and succeeded only in the rules and the principle, but failed in the dimensionality. I didn't care for the fancy camera angles and the tacky-looking cartoonish environments. The birds-eye scheme of the Black Isle games is much better and more traditional RP-style, in my opinion. I like having a party of five characters, too. Each one can become specialized, and you can get more later to replace them. So awesome.