if you're coming from a long break and got used to Sins 1.0 then there are alot of noticeable changes.
the whole balance between lights, flaks, LRFs, and carriers has been tweaked ALOT.
lights aren't explicitly changed much but their relative utility is different than it used to be. people are less likely to just mass pure LRM's so you can get more mileage out of lights than you used to. still not a good ship to mass though as they just don't do that much damage. still pretty effective counters against support cruisers though.
flaks are generally nerfed. they now do much less damage to everything except fighter squadrons. they're still very durable and still very efficient at destroying fighters (and noticeably less good at destroying bombers). its now very much a support ship and not a counter against LRM's, which was its role in Sins 1.0
LRF's are rebalanced in alot of different ways. Javelis and Assailant are almost the same, just a wee bit more expensive to build. Illuminators have been tweaked alot. They are now the most powerful Long Range frigate (and the most expensive and highest tech tier). You can build a pretty effective fleet out of LRF in the early to midgame now but they get torn up by carriers in the mid and late game, so keep that in mind before you commit too much on them.
Carriers have been changed alot. Compared to Sins 1.0, carrier cruisers are now about twice as expensive but carry more squadrons (2 squads for TEC and Vasari, 3 for Advent). The squadrons themselves are a bit more durable and deal a bit more damage. The overall effect is that most late-game fleets are dominated by carriers and lots of squadrons. Fighters rip apart any light armor stuff (LRFs, support cruisers, bomber squadrons) and bombers take care of the rest (heavy cruisers, cap ships, structures).
more than anything you need adequate fighter squadron cover. fighter squads are the best fleet defense. they work much better than flaks and are powerful on offense as well.
