I kept out of this thread, since I had only looked at Polar in Testing Grounds until this morning.
I have now played 6 matches on it and I love it.
Cicada 6 MPL
Glorious. Run around half the map, got into the back of the enemy firing line and wreaked havoc (sure, I died after killing a Timber, I think, but half the enemy team turned to face me the rest of my team got some free shots in)
Quickdraw 2LL, 2 ML, 2 SRM-4
Lots of fun, stuck with the big guys and when the fight was joined, moved to the sides to get some shots in from a slightly different angel (lost that match, but it _was_ a ton of fun)
Grasshopper 2LL, 4 ML
Insane fun. I
_flanked_ in a 65km/h Grasshopper, lol. I was LMAO sooo hard (not because of - what´s the English word for "Schadenfreude"? - but because it was something _unheard_ of in MWO). Game ended in a 10-12 loss, but man, I had a blast
Cicada 2LL, 2ML, ECM, Conquest
Not a lot damage done (some 150 or so - LLs were essential to hit those targets of opportunity while running from cap to cap), but oh was taking away the enemy´s caps fun (yes, the enemy team basically formed a death-ball - and I don´t think that works on Polar-Conquest

)
Cicada 2LL, 2ML, ECM, Skirmish
My best match on that map yet.
Giving ECM cover to the big boys and assisting them with laser fire for most of the match, flanking like crazy in the later stages
Almost 650 damage, 2 kills, tons of assists
Conclusion:
LRMs:
Didn´t had much of a problem with them. (I _did_ have either ECM or Radar Derp, so take that with a grain of salt). Using them also didn´t feel all that OP to me, most enemies were quite good at shaking my locks. In my Griffin game, we had ONE enemy being pummeled to scrap by LRMs, but he was alone, engaging an Ebon(?) at close range and was hit from 3 or 4 mechs with LRMs (not necessarily boats, though) at the same time.
Brawlers:
Can´t speak for the truly slow ones (50kph or so),but if you can get to 65kph or more, not a problem. Flank the enemy and hit their rear.
Long-range poking:
This will get you killed - fast. I have seen a lone Timber standing in the open getting pounded to scrap in what felt like 5 seconds - but then, this probably goes for _any_ map. (if the whole team does it, this might work, don´t know, never played group)