I thought London Heathrow Terminal 3 was quite a nice building once airside, some places for descent views, which are probably better during the day- not at night or during the evening. Just as good as Terminal 4 & Terminal 5.
I thought the Airbus A350-900 was a brilliant aircraft having flown it. Finnair as an airline was absolutely brilliant, very friendly staff. I am pleased they offer free Tea or Coffee at least, don't mind paying for the extras.
Helsinki airport to stay for the overnighter was a good choice, only one bar was open- but it was quite and I enjoyed speaking to the Barista who was on that night. Enjoyed exploring the Airside of the Terminal- More airports need the charging points that HEL offers.