I have spent countless hours of my life playing Diablo II - and I do mean countless hours (several characters to level 90+), so I can vouch that the reviewers saying "if you like Diablo, you'll like this" are absolutely right.
It did take me several hours to get my head round the game and its flexibility: unlike diablo, you can choose cross-class skills as you want and make varied, well rounded characters. The enviroment is incredibly rich and well drawn, and looks good at resolutions up to 1600x[whatever it is]. The dialogue is well written (unusual for an RPG) and the plots well written. I really can't praise it enough, overall.
The only downside is (to me) an utterly illogical trading system and item management. Whereas the rest of the game is beautifully done, the whole item management system appears to have been written by the work-experience boy on a friday afternoon. Items are dumped one on top another in the inventory, and are so small as to be practically invisible.
On the whole, I would wholeheartedly recommend this game, and would advise anyone playing it to persevere. By the time you are on level 2 of the first dungeon, you'll be hooked and will end up spending many happy hours.
Also, don't be a hero - play it on easy until you get the hang of what you're doing! Once I'd swallowed my pride and turned the difficulty down, the game became a joy to play.