CW has absolutely no Elo balancing. This means it doesn't care if 2 days old newbros or 3 years old veterans with 140+ 'Mechs and a shit bucket beside them are pitted against each other. If you're not prepared for it, or if you have no idea what you're doing, it's your own problem . . . with consequences for your team. This is especially a problem if you get placed in a pug team but also if you face a pug team.
In our first matches with my unit, we faced nothing but unorganized pugs. The worst of all, we were defending as Clans the whole time. The same thing happened in each match; the puggies hit one gate hard but once we dealt with them, the pressure was relieved instantly never to pick up again. Every single one of them started doing their own thing; attacking gates one-by-one, doing suicide runs and generally being unorganized. Each match ended up us pushing to the enemy spawn in sheer boredom. We kept winning by ridiculous scores like 48-6 and a one-sided match like this wasn't enjoyable for either side. I was on the other side of this massacre as well. Being in the middle of headless chickens doing random things, it's infuriating.
Clicking the CW tab should pop up a warning about the possible horrors you might face and the trauma you can inflict upon your teammates.
The builds - "The horror, the horror . . . "
One side effect of no-Elo matching is that you keep seeing builds 'Mechs that make absolutely no sense. Griffin with an ERPPC and a Flamer, numerous STD Spiders, LRM Atlases, XL Atlases, XL LRM Stalkers, AC20 Centurions trying snipe outside range . . . and trials, trials everywhere. I see weird stuff all the time in the solo queue, but I've never seen such silliness in such dense concentration before.
Clan lasers are awesome
It seems like Clan lasers absolutely rule the CW arena. Being able to dump 50-70 alphas out to 400-800 meters repeatedly in a tug-of-war is just devastating. I've never been a fan of C-ERLL's before, but these things are just insane in CW. With the range module your optimal max goes up to around 800m and the IS has absolutely nothing to match your damage at those ranges. Only dual Gauss builds can hurt you and at 800m you can actually avoid the Gauss projectile. My Warhawk with Gauss+3xERLL's repeatedly pulled 1600+ damage matches in defense. If you stand at the gate, you can even start damaging the enemy as they drop out of the Dropships. They're insane.
(U)AC5's hurt, a lot
The only time our unit(4 man + pugs) lost a match was against an organized team (6 man+ pugs) that brought a (U)AC5 heavy deck on Boreal. They kept themselves in cover at the sides of the gates, but they quickly formed a line when a push happened. Anything that came out of the gates quickly melted under fire from BNC-3E's, Ilya's, Shadowhawks, Dragons and there was even an insane Jager build with quad UAC5. Seriously, embrace the (U)AC5 as IS. It's one of their best weapons against the Clans.
Attack deck ≠ Defense deck
As expected, attack decks don't work in defense and vice versa. When I brought my snipy Warhawk to an attack, I was doing well wearing defenders down and killing one occasionally, but I realized I actually did little to reinforce the attack. Plus, I felt like using snipy 'Mechs during an attack detached me from what my team was doing. The next time I brought a medium-close range deck with the dreaded TBR-SCR-SCR-SCR combo and I was much much more useful to the team.
Clan heavies and the Stormcrow rock for attacking
Considering the 240T limit, which boils down to average 60 ton per 'Mech, I think the clans have a great advantage when attacking. While attacking, you need mechs that can tank a lot while also having firepower and some mobility. IS has to bring Assaults to fit that bill and bringing an Assault means you will have to bring sub-optimal lights or mediums later. Therefore when IS attacks, if you manage to take out their Assauls you know they'll run out of steam shortly afterwards. IS heavies are mostly played with XL and with the exception of the Orion and TDR, none of them are particularly tanky. They're glass cannons and you don't want to bring glass cannons to attack a dug-in enemy.
Clans? Around the 60 ton mark they have so many great 'Mechs that they can keep the pressure up, up until the end. SCR+SCR+SCR+TBR, SCR+SCR+HBR+HBR, SCR+MDD+HBR+MDD . . . these are all amazing combos that the IS can only defeat with superior skill and coordination.
One thing to note is the situation of TDR's for the IS. These 'Mechs with structure/armor bonuses and ridiculous weapon quirks are just a pain to deal with for the Clans. Bringing as many TDR's as possible is a great idea for attack. It has even been blessed by its own Clan whine thread already.
Remember how I said I felt detached from the team when I was in my snipy Warhawk? You can do great sniping/lurming and dealing good damage hundreds of meters from the gate when attacking, but it doesn't mean you're contributing meaningfully.
I had a particularly frustrating match yesterday in a pug vs pug match as an attacker. At first we seemed to be doing okay taking down gates quite fast and even pushing out slowly, but after the first wave our coordination bottomed. I decided to take try my luck and rally pugs for an assault to a side generator. Thankfully I could reach out to about 5 players and we pushed to the generator, taking it out before their brawlers came and finished us off. At this time, we still had 'Mechs hanging out by the gates while I was screaming for help for the push in chat. With some great sacrifice (and some carrying on my part) we managed to take out the other gen as well. At this moment, we bled the enemy dry, but they dropped a fresh crab with dual AC20's that blocked the last mini-generator completely. When we dealt with that Crab and generator, my Timber was down to 4% health with about 1 minute remaining to take out the Omega. The match ended with 25% of Omega's health remaining . . . I was still happy that it was such a close match until I looked at the score screen. At this moment we still had 3 guys with 2 'Mechs remaining that did nothing but hang out near the gates. I was really disappointed.
TL;DR: It's a good idea to preserve your 'Mech in defense as long as possible, but on offense if you still have 'Mechs(especially assaults+heavies) by the time the round ends, you're doing it wrong.
Lurming matters, but when?
I think LRMs are great on the defense. Especially IS LRMs hit really hard and I've been extremely annoyed by the numerious AWS-8R's, Stalkers and HBK-4J's out there spitting out unending LRM streams. There is little cover on especially Boreal so you either get lurmed to death, or you manage to find an ECM 'Mech nearby. It's also a great way to dispose of Clan Assaults, which are just huge LRM sponges with their silly roofs. Bringing a TAG seems to be essential considering the number of HBR's out there though.
On the Attack, I think you should ease up on the LRMs. They're useful in getting rid of turrets and generators from range, but mostly the defending forces have sufficient cover or hang out near big objects in order to break locks quickly. You're better off bringing direct-fire weapons and taking your place at the front lines.
Disregard Atlases, bring King Crabs
Atlases can be great to throw at your opponent to stall them for a while, but they're not that useful otherwise. These behemots suck at fighting in the open, uneven ground due to their hardpoints. King Crabs have similar and better hardpoints but instead have ridiculously high mounted energy hardpoints and the best of all can bring dual Gauss to the field. You can hill hump with ERLL's and dual Gauss meaty targets. AC40 Crabs are also awesome at defending the last objective.
I don't remember being threatened by Atlases at all, but I've been hurt a lot by Gauss Crabs and and AC40 crabs. CW maps favor range and direct firepower and the Crab is just better at range.
Queue times makes you productive
This article has been sponsored by the low population of the CSJ.
Lastly, CW is amazing
The battles have a meaning, you get to have constant 30 minute action instead of the usual 2-3 min wait + 5-10 minute match combo, tactics and roles matter, your 'Mechs matter and the pacing is awesome. I really love the idea behind CW and I can't wait to get more matches in. I hope PGI realizes the potential and further improves the CW.