Season 7 was most interesting for introducing new attorney Jamie Ross, after the sudden tragic death of Claire Kincaid at the end of the Season 6 finale "Aftershock". It is also the second season to have Rey Curtis as Lennie Briscoe's partner, he and the chemistry with Briscoe took time to settle but by halfway through both gelled a lot better. "Causa Mortis" was actually when first getting into 'Law and Order', via the Briscoe and Green period, one of the first early seasons episodes watched.
'Law and Order' fared very well when it came to the previous season premieres, the weakest being Season 5's "Second Opinion" which was still good. My memories of "Causa Mortis" were very positive, while not considering it one of the show's best or most memorable. Seeing it again for the third time recently, it still is very good and actually better than remembered. Change is always hard and unsettling and "Causa Mortis" didn't do too bad a job. As far as Season 7 goes, it is around high middle category in ranking.
"Causa Mortis" isn't perfect. There is a loose end regarding the cassette tape in who extracted it (not explained, seeing as it was impossible for it to have been the victim) and why it was unrealistically treated the way it was by the killer.
Although Carey Lowell portrays Ross very well, she and Sam Waterston (even for two characters that don't get along here and where McCoy is struggling with coming to terms with the events of "Aftershock") don't have much chemistry here, too clinical and dismissive somehow.
However, "Causa Mortis" does a huge amount right. The production values are solid and the intimacy of the photography doesn't get static or too filmed play-like. The music when used is not too over-emphatic and has a melancholic edge that is quite haunting. The direction is sympathetic enough while also taut. The script is typically, certainly for early 'Law and Order', tight and thoughtful. Standouts being the "I believe in monsters" line (one's on the same wavelength with Ross here) and where Curtis mockingly references Alan Dershowitz while also perfectly summing him up in the process.
The story is very intriguing with a very harrowing beginning and lots of intrigue in both the policing and the legal scenes. Will agree about the motive and the reaction of one of the characters when hearing of it being truly chilling, ended up hating that character just as much as the killer at that point. The acting from all the regulars is excellent and support is with no obvious complaint either.
Summing up, very good start to Season 7. 8/10