Sona's good in big teamfights when hopefully your team is grouped and close enough to take advantage of the retarded base bonuses from her auras. Q aura lategame at least helps you instagib single targets during hard engages, and the shield aura procs Ardent Censer which is basically like old Zeke's Herald which was an Attack Speed aura and completely OP for taking objectives, so she has that going for her. E aura still is pretty lame until you max CDR, though at least you can use it to dodge things like Ashe Volley on reaction which I guess is okay.
You actually have slightly better trades earlygame if you max Q first than old Sona given Q auto earlygame does more damage, meaning new Sona is even more focused on level 1 lane cheesing basically. Furthermore Sona's level 1 invade is RIDICULOUS because Q gives like 260 magic damage for 5 man invades. The worst part is because you don't get free stats from Q aura, it means you're rewarded less for really persistent kiting from both you and your AD.
idk, new Sona is okay, even factoring the 50 range nerf on Q. But her kit is just so...abuse heavy. It's like Riot wants Sona to be a bunch of silly flashy gimmicks. Also you effectively are forced to build tank+max CDR on new Sona most of the time so that you can actually take advantage of auras, which do have really silly numbers. Earlygame though, you need AP runes/masteries to make your trades matter.
Matchups:
Leona: Same as before, actually one of the few matchups you probably do slightly better in given Leona offers nothing to her lane except her ranged engage combo, and new W does slightly better for mitigating burst when Leona does manage to engage and I guess if you like, new E is a bit better for reaction dodging Leona's dash. You always have dumped on her at level 1 by just full focusing her AD before they hit level 2. If you didn't win the lane by then, you played it wrong, but you still have a window post level 2 to crush this lane while your Flash is still up, given you can survive a Leona engage guaranteed by Flashing out of it which should be enough time for you to harass adequately.
Thresh: Matchup is harder because MS quint Sona isn't as good anymore given you don't get free stats from Q aura anymore which means your range AD isn't as threatening while kiting. Still a fair matchup as long as you don't let Thresh walk up Flay earlygame.
Braum: See Thresh. This lane used to be a lot better for Sona where you pretty much trolled him with MS quints and win by free poke, which overall became weaker because no free stats meaning Braum gets more effective sustain from timing his shield in this lane now.
Caitlyn: Bah. Caitlyn is stupid to play against now due to your mana costs whereas previously old Sona hard countered Caitlyn by being an unkillable lane that couldn't be forced out early. Sad times. Now you basically have to rush Chalice to manage the lane consistently.