Haven't tried the new Gauss yet, but I don't think I'll like it. My absolute favourite is probably Heavy Lasers. Takes a while to fire, but during that time people die if they don't twist themselves. The cooldown gives you plenty of time to focus on repositioning. Have been using them on my Shadowcat, Hellbringer, Timberwolf, basically anything that had the space and heat available. IS ERML have also gained a lot of favour, as the new best weapon to combine with LPLs. MRM and ATM feel very different from existing missile weapons and very satisfying to use. They are HEAVY though... but great alternatives for the older systems. My 2xPPC, 2xMRM30, 4LMG Mauler is a blast, and my previous TBR with SPL and SRM6+A has been replaced by a more rewarding ATM30 (2x9,2x6) and 5xcHSL to use within the minimum range of ATMs. RACs have been very situational for me. They're definitely very damaging, but more of a support weapon than something to use when pushing and you need to twist your torso. LRMs finally have a ballistic counterpart in terms of annoying cockpit blinding though, I wish I could reduce the explosion visibility instead of the shake. Honorary Mention for the PPCs, Which I'm starting to use more often. HPPC is DEVASTATING in my KGC and the Light PPC is very nice to boat 3 of in my arrow. Also, UAC2s I've enjoyed alot, but UAC20s aren't my fancy. Same with liking LBX5s in the Ilya Muromets, but the LBX20 just takes up too much space to be fun.
I think overall the new IS ACs and ER mediums, and the Clan heavy lasers, are the better weapons introduced this patch. The MRMs and ATMs are a bit meh.
Confused... wait you all meant the Light engines and ferro light (as it enables all my weapons)? Most of the new weapons are too situational for my liking. RAC's just have the flinch advantage - I really want to like them as I love triple UAC 5 JM6's etc but I struggle as the negatives are just too much. Totally support weapons. IS ERML are very nice though but mainly because they match up to the LPL so well. Light PPC's work very well on lights. UAC 10's work well as main weapons. Its technically not a weapon but the TC 1 is something I'm using frequently. Not tried the clan side since PTS so no comment there.