Greetings.
Sorry for the long time, I can only access the internet while at job right now.
That being said... Wow, I can finally a bit more about one of my favorite bands ever, from any musical style I listen to.
One thing : Dies Irae is the last album they ever made (out of four/five, I'll explain why) is, IMO, the easiest to get into. Not necessarily the best, but probably the most "upbeat" album Mr. Doctor ever made.
By chronological order :
-"The Girl who was... Death" : What a good first album... As strange as it may sound, the concept of the album is based upon the old series called "The Prisonner" (with the famous quote "I am not a number !!!"). I love that album very much ; the feeling, as expected from DD, is a very complicated mix of anxiety, theatrical grandeur, fear and nevrosis. The Highlight of the album : about five minutes after the start of the album, there's an AWESOME violin solo (fast and furious) that makes the album worth it. It's pretty hard to explain this album, but I think it could be a good purchase to introduce your friend to the band.
-"Eliogabalus" : Probably the "least good" of all, though it's still excellent. It's the only album with two distinct songs ("Mr. Doctor" and "Eliogabalus") ; all the others are only one big song. The mood of this album is quite different, it's more quiet, it's less "big" than it's predecessor and the ones following it. Nonetheless, it's not a bad album, far from it ; I would simply not recommend it as a first buy.
-"Sacrilegium" : This album would be my pick as the most frightening the band has made. It's back to the style of the first album, with maybe a little more budget. There's a choir once more, as well as an orchestra (although it's not as bombastic as Dies Irae). The lyrics on this album are awesome by the way. I think it would be the best choice to buy to your friend, as this album is a grower, hard to get into at first, but hell it's good when you assimilate.
-"Sacrilege at Fatal Arm" : Now this is hard to find, but if you ever see it, BUY IT. Believe me, you will not be disapointed. It came out after Sacrilegium, it uses all of the previous album's musical parts but they are mixed differently (aka not in the same order) ; plus this SaFA has even more music to it that weren't featured on Sacrilegium. If I remember correctly, it runs around 65 minutes, and then there's a bonus track hidden after four minutes of silence (the same bonus track as Sacrilegium). This album is in fact the official soundtrack of a movie Mr. Doctor made for his university (did I mention this guy is really a doctor -- twice ?? Got a doc. in philosophy and criminology). If I have to compare Sacrilegium and SaFA, I'd prefer the last one ; I think it's mixed more effectively to create the atmosphere he really wanted in the first place, and the additional musical bits are really good, not just filler IMO.
So my verdict would be :
1. SaFA
2. Sacrilegium
3. The Girl who was... Death (although #2 and 3 could be replaced by the other one I think)
Hope this helps Melancholia, although I think I was a bit incoherent. I'd like to know wich one you bought and what was her comment on it,
I've been always called "False metalhead" "raver" etc by lovely friends,but i never really mind...At least I am still listening to metal unlike most them 
