Noah Gibson-Baker’s review published on Letterboxd:
Sweeney Todd tells a great story with good characters and fun gore, but in this review I want to focus on the most important part of the show and film, music.
The music in Sweeney Todd is phenomenal, yeah some of the song writing and performances could be improved, especially Sacha Baron Cohen, Helena Bonham Carter and Alan Rickman. Their line delivery was sometimes awful, but mostly decent. The music is amazing despite these two problems, it is so complex and was obviously planned out from the start with the use of dies irae playing such a prominent role in the films storytelling and character development. Dies irae is a piece of music that has been used to represent death since the 13th century. From 15 leitmotif 13 of them have some correlation to dies irae showing that Sweeney can't escape death, it's all around him everywhere he goes. There is a fantastic video about the music in Sweeney Todd by "Sideways" on youtube I would recommend checking out. I would explain the things he explains myself but trust me you don't want that, plus he does an infinitely better job.
I've heard this is a brilliant adaptation of the stage play but I have never seen the stage play so I cannot confirm this for myself. Apparently there is a lot of 4th wall breaking in the play which I'm not a fan of a lot of the time.
The practical effects are really good and satisfying but CGI is used some of the time and it looks significantly worse.
I would highly recommend you check out Sweeney Todd: the demon barber of Fleet street, I think it's pretty amazing and I love music so this is kind of a no brainer for me.