I was in the lounge yesterday but didn’t realize it was opening day, otherwise I might have paid more attention. I was in the lounge for only ~10 minutes to grab a quick coffee. The food was indeed nothing to write home about. I think there was a shower or two, with a similar system to ones in the non-Schengen lounge. The lounge has great apron views, and it was very quiet when I was there around 8:30 in the morning. Frankly, overall, I think it’s a fine place to wait for a connecting flight, but given how efficient Helsinki airport is, if I were originating in HEL for a Schengen flight (and with priority access), I’d just aim to arrive at the airport 10-15 minutes before boarding. Not worth arriving at the airport early just for the lounge.
Having also gone through LHR, AMS, and ARN all in the span of a week, HEL truly is a dream of an airport, now that the construction is pretty much finished.