Unless they do some serious balancing on the (only) melee class, the game will die in multiplayer ignominy as everyone starts to play one.
Think HARD about the multiplayer games you play... if you were:
1) unbeatable in melee (presumably, since the others are ranged classes),
2) had three times the maneauverability of any other class (jet packs are awesome), and
3) could probably get away from any combat you were losing until the odds were stacked in your favour again,
would you play any other class?
I might... because I'm a masochistic moron in games like this (the fluff says Tac's are more experienced and better trained than Assaults, so damned if I'm playing anything else!
). But I seriously doubt the majority of the screaming fanboi's would.
So yeah... MP is going to come down to the melee balance.
I'm not even going to start into comparing a bolter to a lascannon until the melee is balanced.
