A stupid, yet very interesting question

[the Langolier]

By the way another question  :D We both have Diablo + last patch installed. Is there any free add-ons which could be good to install ?

Well, there are none that you can use to play with on battle.net, BUT there are mods (short for modifications) for the game. Information on them can be found in the mods section of this site. Essentially what mods do is change various aspects of the game like monsters, items, magical attributes and more. I wouldn't worry about them too much just yet; Diablo itself is good enough to keep your attention for a while, but mods can provide an interesting take to the original.