First things first I am not bitching about our effectiveness, god knows we do ridiculous Damage at the moment and are Gods in PvP if played right.
What I am bitching about is the fact that Arcane isn't fun to play. Just being good at DPS isn't really enough for me. Big numbers are fun sure, for a bit. But Pushing AM or AB just feels like a damn chore now. I understand they want us to manage our mana, and I know for a fact that it will be vitally important to do so in Cata (though at this rate frost is actually the best PvE and PvP spec on beta) but it isn't FUN to push AM. It isn't interesting in anyway shape or form to occasionally hit 2 instead of three, ESPECIALLY when 2 does crap damage. I would gladly take a hit to AB to make my missiles hit harder again.
The need for self reliant damage reduction is very real in beta and frost has great options for that. So it becomes a solid balancing game around throwing up Ice Barrier or continuing to DPS. In addition frost gives you loads of options to maximize your DPS. Making sure you are on top of your FoF procs, throwing those ice lances at the right time, using deep freeze when ever you possibly can, even occasionally using your pets frost nova to give you some more damage on adds and trash.
Sure Arcane has Mana Shield but that is mana you simply CAN NOT loose as arcane. Your options are overly simple. AB or AM, with an occasional Arcane barrage on the move, that is IT. There are no other methods you can use to help give you a bit more damage (specifically I mean bread and butter type abilities and not cooldowns), or decision to be made using a GCD to help you survive vs taking advantage. That isn't to say that MAGES don't have survivability options in general but that frost simply has everything an arcane mage would have and then some. Not to mention a mechanic that due to it being reactionary makes it more interesting on a moment to moment basis.
Arcane missiles are not much more than uninteresting, un-exciting necessity and it's really your only other MEANINGFUL option. Sure you could Barrage but you won't unless you have to move.