This is a good idea but this could cause some problems. Depending on what the achievements require us to do, this feature could 'up' the game or ruin it.

An achievement we wouldn't want is one that requires us to kill a specific boss without dying. People would most likely run off if the situation got bad for them. That isn't team play.

Now something that would be fine is an achievement that requires you to kill a specific boss with a full group and all players in the vicinity, alive. You can die but if you run back in time or someone revives you, everyone will still be eligible to receive the achievement. If just one player is dead or is too far away from the defeated boss, then your group doesn't obtain the achievement. This would require players to use teamwork.

Simple achievements are great, too. For example, revive a total of 50 players. Another one would be to deal a total amount of 9000 damage to enemys. I would name it, "Over 9000!"

See how these work out? Achievements are fine as long as they are obtainable from using teamwork, playing, and enjoying the game.