You'll hear all sorts of opinions about Diablo 2. Personally, I liked it. And this isn't just a case of, "if you liked Diablo 1, you'll like the sequel." I thought that the first Diablo was a fun game, but it had too many flaws. D2, therefore, is a really fun game that fixes lots of those problems. You have more choice for your character -- each "archetype" has a distinct playing style and more skills that you can specialize in without replaying the game. The original Diablo was also pretty repetitive. You fight your way through dungeon level after dungeon level, with your only reward being a subtle graphics change every 5 levels. In D2, you go between huge wilderness areas and cramped dungeons. Different places have very different feelings to them -- both their visual appearance and their strategic layout changes drastically.. as do the monsters. I didn't get bored nearly as quickly as I did with Diablo.
Of course, you still will get bored eventually... This is still a point-and-click, hack-and-slash game at heart. But I easily got my $50 out of it before I stopped playing.