I have some recommendations for you all on what to play in preparation for D4. Well, just keep reading.
Of course, playing the games would help you get immersed into the story a lot more, than simply dropping into D4 without any prior knowledge or connection.
Diablo I is probably too old to play at this point, unless they release a remastered edition someday. Instead I would strongly recommend...
PVP Changes
Wintergrasp will no longer be fought on a per realm basis. When it is time for the wintergrasp battle, players will be able to queue and enter an instanced version of the battle ground. As long as ONE person on your faction participates in the battle and wins, your faction will have access to wintergrasp fortress and the Vault of Archavon raid. The fortress will be PHASES per...
Putting aside our prior warning that there are quite a few good classes in Lost Ark (and all of them are viable), the lists above should give you a pretty good idea of where each class stands so far as the overall rankings go.
Simply put, Bard and Paladin are kind of in a tier of their own due to their viability in both PvE and PvP scenarios. Some players are just not going to enjoy playing...