Lord of Destruction (most commonly referred to as LOD), was released a few years ago and was an instant hit as it expanded upon the already widely popular Diablo 2. One of the immediate changes players grew to love was the addition of a higher gameplay resolution: 800x600. It may sound silly, but this was seen as a great 'gift', as players had grown tired of playing at 640x460 resolution. The new look increased the quality of the graphics drasticly and in a sense, sparked new life into the game [but obviously, it was already doing very well without it].
Content wise, there were a lot of updates and new material to play with. Two new classes were made available to players, the Druid and the Assassin. The Druid seemed to be a bit of a mix between a necromancer and the Barbarian as he was able to summon but was also quite effective in melee combat. The Assassin was a bit more difficult to categorize, as she seemed to be more complex and using relatively new gameplay/combat concepts. The use of traps, although interesting, was totally new to gamers and it took a little while for players to notice many Assasins roaming around [one of the perks people found very enticing was her use of claws. Rawr.]
Probably the most important and highly anticipated new content would have to be the latest act, act 5. Pitching players against Baal in, what was, a totally new environment and landscape filled with incredible creatures and interesting quests. The difficulty level of this new content was seen by many as being bellow act 4, but appeared by many as being more fun.
Other anticipated additions were the inclusion of a load of new items and as well all know by now, items are what have kept Diablo 2 so popular. People just love item hunting, finding the rarest and greatest loot known to mankind. The extra equipment was a godsend for many hardcore gamers. [and the increased stash size was also a welcomed development]
The addition of runes was an interesting one, as it did add extra items to be found and also allowed the improvement of all items [including pre-Lord of Destruction].