As a Londoner I think they did as good as job as time and budget could allow, like you say (shame that I *always* spot an individual walking through the back of one of the empty shots, I guess it could be a ragified Zombie !).
There's something about that cover I really like, I have to say - the stillness and the sunhaze warms you into it and does exactly what the film does, gives you a sense of forboding that something must be wrong, but you can't quite put your finger on it ! ('why is he wearing a hospital gown ?' the uninitiated would muse...). Perhaps making it more "horror" or overt would blunt the subtlety ?
Just a thought, love the edits and the klokwerk art, so won't complain either way whatever you go for - just know there will always be permanent webspace
