S9 was not good, but Milioti's presence almost single-handedly made it worth watching, and was honestly worth the 8-season build-up. Her rendition of 'La Vie en Rose' is genuinely beautiful.
Ranking the main 5: 1) Smulders 2) Hannigan 3) Harris 4) Segel 5) Radnor
None of them are exceptional, but I like Smulders and Hannigan quite a lot. Harris pisses me off frequently, but there's no denying he has a lot of charisma. Segel and Radnor have many fine moments throughout, but generally didn't care much for them - Segel at least has been great in other things though.