I am a danish Villa fan who knows him quite well, even though he isn't someone who has given many interviews.
First and foremost it has come as a big surprise in Denmark that he has been able to land such a job. Contrary to many reports he wasn't responsible for the transfers at FC Copenhagen. Copenhagen's long term manager, Ståle Solbakken, is the one who is taking care of those mainly, but Lange has been assisting him. Therefore it also seems a huge step going from being number 2 in Copenhagen to being number 1 at Villa, if we assume that his role is more like a european-type sporting director who is responsible for transfers. That is the model every other club than Copenhagen for example uses in Denmark.
His reputation in Denmark is honestly mixed. Copenhagen have in recent years not delivered great, and particularly this season has been poor, where their recruitment have received a lot of criticism. They have by far the biggest budget in Denmark, but seems to have been at least momentarily overtaken by Midtjylland, who is also owned by Benham, the Brentford owner. Midtjylland, like Brentford, have a very statistical approach to the game and signings, which seems to be working quite well for them, whereas Copenhagen's recruitment is more of a mystery to me. In recent years Copenhagen has focussed mostly on the danish leagues but have also bought players from around the continent. Some have been a huge success but many also a failure.. I honestly don't know how they decide which players they are signing, but I have a feeling they focus on scouting the players on scene. However Copenhagen also has a very particular way of playing, and I assume it is important for them to know that players fit into that style. However, I have also seen him described as a "data nerd", but I am not really sure which approach he prefers.
A part of his job he has done very well however turning Copenhagen's youth development around. For many years they weren't really producing anything, but in recent years they have had very good players come through and are now considered one of the best academy's in Denmark. To my understanding he has been the main guy responsible for that. I do think that he seems very intelligent, and he comes from an organization which for many years have had huge success. I would say that i trust him in terms of improving the organization and creating a more defined strategy for the football club. However, if you asked me who I wanted to be the one spending the 100 million we hopefully gets allocated this summer, then he would be very far down my list.