I fly 3-4 times a year from either ORD or JFK to China r/t. I've been flying AY J because of the significant $$ savings, and the increased EQD and EQM earned.
While I don't really care for the A330's seats, the A350's are decent - and for the savings and benefits, I can live with the A330. I need to sleep on the HEL-China flights (CAN / PVG / PEK) because I typically have to hit the ground running as soon as I land, and the A350 seats are good enough to sleep in.
I've never bothered to venture into Helsinki during the layover, but I have done overnight stopovers on the way home. Uber works well there. Visit Fazer if you get a chance!
They have a decent lounge in HEL with nice showers.
The AY airport staff, flight crews and lounge staff have always been super friendly and helpful. If you do venture out during the layover, they have a priority security screening area upstairs, and it's always been empty when I've been there.
I don't fly for the food, and most of the time I don't eat much but a snack on the plane, so I can't comment much on the food, but the folks around me seem to enjoy it. I do know you can get a burger at any time, which I have taken them up on.
You can check out their menus here:
https://www.finnair.com/en/nordic-kitchen
One last thing to note - over the course of probably 48 AY flights, I've never had any of them post to my AA account without making a missing mile requests and follow-up phone calls to the AAdvantage desk, so save your BP's! AA's told me many times that AY and BA are horrible with posting to AA.
If you have any specific questions , feel free to ask.