If you're looking for a unique twist on the Diablo-esque action-RPG genre, Sacred definitely fits the bill.
The variety amonst the characters is probably what sets Sacred most apart from Diablo and its kind. Everything from Demon, to Seraphim, Vampiress, etc., there is just a bunch of unique and interesting characters to play. And of course there's the traditional Gladiator/Warrior type if you just want to hack and slash your way through.
Next up, the graphics. They are actually quite detailed. Much moreso than say Diablo 2. And the particle and lighting effects for spells and such is really cool looking. That's half the fun of being a Battle-Mage; just watching your spells go off.
You can also string together combo-moves from the combo master trainer. This is a very interesting and unique dynamic.
The weapons offer a good variety. There are a ton of unique weapon models, and various attributes assigned to the weapons to further customize them and make them unique from one another. There is a lot of variety to be found and pick from. You can even buy a horse if you so desire and engage in mounted combat. It's really quite amazing the features that are offered in this game.
Sacred is probably the most under-appreciated action-RPG. Not very many folks talk about it or probably even play it, but that's a shame, because they are missing out on a great game.
The world of Sacred is also HUGE. One look at the in game map will let you know that it will take you a very long time to run through all of the content this game has to offer. There are plenty of side-quests in addition to the main quest as well, which is always a good thing. The more the merrier.
All in all, I'm still playing Sacred, and IMHO it's a great game. And considering that you can purchase Sacred Gold (Contains Sacred and the Underworld expansion) for probably dirt cheap nowadays, you owe it to yourself to experience this wonderful gem.
In many ways, I consider it to be superior to Diablo 2. Do yourself a favor and pick up a copy :)