Diablo 2 has a very good system,but become very boring after few days of gameplay.
When time to next level is aproximetly two days I need another motivation than level-up.In most RPGs I found it in story or sub-quests,but this was missing in Diablo.And killing Baal twenty times,too see if he dont drop at least something usable this time is just boring...
However I like mods for Diablo 2 (Zy-El for example)...