I’ve made several posts on this site about how good Finnair’s longhaul product is (in terms of value for money) and how it is improving with the installation of lie-flat beds.
It is not the greatest product in the world, but for what you pay it is more than acceptable. I would just try to avoid the MD-11s if possible.
MichelAngelo is right about the short-haul sector from LHR, but it’s not quite picnic standard though!
The new Via Lounge and Spa at HEL is excellent, as is the new longhaul terminal extension, all of which makes HEL a very easy and pleasant airport to transit.
If you have a look at Finnair under the Airlines category on this Forum, you’ll see other threads on which I’ve posted.