I think it's probably really good to be Patti LuPone. I just get that impression.
I'm a little out of my depth discussing the current revival of Sweeney Todd (which seems, by the way, to have inspired a movement, or the beginning of one: the upcoming revival of Company is also done in the DIY, company=orchestra format.) I know opera people are obsessive about their rep, but seriously, queens that know their Sondheim know their Sondheim. And though I like him lots, I'm pretty much limited to having seen a live production or two and worn the Len Cariou version of A Little Night Music down to a scratched plastic coaster. So this is I suppose today's caveat lector: your mileage may vary, as the young folk say.
I did in fact see Lyric Opera of Chicago's big, confused musical-qua-opera staging of Sweeney a few years ago, so I've got that to compare to, but they're so different it's almost laughable to compare them. Terfel sang the role in a way Michael Cerveris simply can't, and on the other hand played it rather generically...I've never really been able to hop on board the Terfelwagon, and unlike so many, I dread the idea of his Wotan. It's quite a voice, but I've never been able to warm up to his "best kid in the drama club" characterizations. Also in Chicago, Judith Christin did a creditable job of what I have it on good word from a more versed Sondheimer every Mrs. Lovett until LuPone has done: a really passable stab at being Angela Lansbury, the UrLovett. There are many worse people to be, and it's not really anyone's fault that her portrayal is an immortal moment in theater. It takes guts to try something totally different and (in addition, I suspect, to smart direction) guts are a strong suit chez LuPone. And she looks fantastic, by the way.
The production itself is radically spare and at the same time looks like an ingenious act of trickery. The cost, I think, of wrenching Sweeney out of the rut that is the heritage of a fanatically beloved first production, is a certain lack of fun here. Nuh huh, I know it's about murder and stuff, but Lansbury and Cariou don't gild the tuberose: they are sinister and Mephistophelean, but in the way of 19th century Mephistopheleses(eseses), evil with a glint in its eye. That glint is dead in the current staging. Which sounds like a diss, but it's not. Going to this Sweeney is, opera-wise, more like going to Elektra than Don Giovanni, if that metaphor does anyone any good. It's about people doing bad things because they're human wreckage.
Cerveris plays Sweeney as a walking corpse, and as for LuPone...I think there's something quite complex about her portrayal really. It's dire, but it's also a little bit Lotte Lenya, a little bit Marjorie Main. (I realize that's a bit far out, but listen to a couple of the no-bull line readings...maybe I'm wrong.) By the same token that her character's fit with that of Cerveris takes away some of the fun in numbers like "A Little Priest" where a darkly funny, game sense of collaboration between the two is replaced by a bloody deal well made and sealed, and perhaps also takes away a bit of the pathos--Lupone singing "By the sea" is just creepy--I think there's an urgency, a macabre radiance here that the original pairing didn't so much have.
Certain gestures in the staging (the pouring of buckets of blood, Mr. Todd walking around with the coffin lid on his shoulder) wear out their welcome a little, but on the whole the economy of the thing is almost shocking. The singing other than that of LuPone is all around B+ material. As Alex has noted, the arrangements, while not sumptuous, do a very neat trompe-l'oreille thing and let you forget quite often that there's a kind of compromise going on.
Lots of empty seats in balcony, so I'm thinking if you want to catch this, you should consider stepping on it.