THE GOOD:This is probably one of the largest, if not longest, Adventure games ever to be produced. The sound, and graphics are quite finely done, and the gameplay is somewhat addicting.
THE BAD:
The game lacks a bit of options. Most of what could be done is just hack and slash, get the money and/or weapon, level up, and beat the game. It lacks diversity.
SUMMARY:
From Diablo
Coming from a Diablo player, the game is a great sequel, and, perhaps, destroyed the image of sequels being uglier than the originals. The additions implemented in Diablo II (D2) are indeed spectacular and have increased the replay value of the game.
I will try to take the game piece by piece to help you decide on whether it's goo enough.
Graphics
Have you seen the graphics of Diablo? They're nothing compared to the models of the different characters. The complexity of the image mapping, or the detail of the characters' clothes, and the shape of their bodies are well done. Comparing the graphics used in the program with those that came out during its release, D2 would have to be at par, if not better.
Sound
The ambient sounds or the sounds in the environment are really cool. Sometimes you would be able to hear howling from a distance. The good thing about the game sounds is that you won't need a good sound card to be able to enjoy it. Some games of today require a surround-capable sound driver for you to enjoy it. If you do have a 5.1 sound system, then it would be a great plus to your game since the game is created in a surround environment.
Gameplay
This is where there's a little problem. The game is very enjoyable, challenging, and exciting to play, but does it last long? If you're a gamer who goes for different tactics and strategies, D2 would bore you out by the time you reach Act 3. Of course, if you enjoy killing different enemies, you would end up adrenalin-charged until Diablo. 
Replay Value
In my opinion, the game doesn't have a good replay value since all you do is hack and slash, or use magic all through out the levels. There's nothing much to do but try to defeat the missions, and increase your level. Since there are 3 difficulty stages, it gets tedious at times.
Network capability
Now, this is the heart of D2. With network capability, you can play online on Battle.net, and beat Diablo with the various players on the server. You can also trade weapons with the other players, or you can duel it out to get all their weapons and items.
D2 is also LAN (Local Area Network) capable, so you can invite your friends over and connect your PC's through a HUB.
Playing in a network, or playing Mutliplayer creates a whole new world for D2 since you have more players to play with or against.
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