Okay, first of all, ToT is a band that has gone through a lot of changes. Whether or not one likes those changes, is a matter of taste and I don't get into that. However, here's a brief summary of their albums:
Theatre of Tragedy: Gothic metal in its purest form. Male grunts and a high female voice. The songs are rather unimaginative, except for "...a Distance there Is...", which is a very calm, long song consisting mainly of female vocals, piano and cello.
Velvet Darkness They Fear: Their breakthrough-album. Otherwise similar to the previous one, but this time the songs are great - far better structured and played. An excellent album if you like the contrast between beautifully angelic and horribly demonic.
A Rose for the Dead: A mini-CD with a couple of songs left over from "Velvet..."-sessions, a couple of bad remixes of their old songs and one nice Joy Division -cover. Nothing very special here.
Aégis: The male grunts are almost gone and he sings instead in a low voice. The music with more acoustics is softer, more atmospheric; although a bit more poppish with clear chorus-parts etc. I know many metalheads, who like this album, however (myself included).
Musique: Okay, the "metal" is finally gone and a lot of electronics are brought in. The soundscapes are less "medieval" and more "industrial". The male voice is closer to the original goth-pop and there definitely are no grunts here.
All in all, ToT have very little fans who like all of their albums; instead, their early albums have a decent cult-status in Scandinavia and nothern Europe, while their latest album has gathered a new and different following. I suggest you download some samples from the net and try them for a while, before buying any of their albums.
-Villain