Don't worry, it doesn't mean the game is over. It doesn't even necessarally mean that anyone has "finished" the material that is currently available. (Although some players probably have seen all the current content.) "End Game" is just a term used to define whatever the current top level players are doing. So at this point in EQ2, it would be used to describe lvl 50 raid encounters.
In another few months, the first expansion will be released and the lvl cap will climb to 60. At that time, End Game will evolve to mean whatever the lvl 60 players are doing.
Traditionally, the term is used to quantify the current level of greatness to which you can aspire!