I initially thought, It's not a big deal. Obviously, a lot of players won't know what to do, as this will be only their first or second stealth-'em-up experience, so it's okay to telegraph the information and clues about Lady Boyle to the players.
And then I played the mission, and I realised there was no need to neon-sign the information.
1. This mission's halfway through the game. If somebody doesn't know by now that they should explore, it's their fault. It really wasn't necessary for multiple people to tell me about the Boyles' diaries. The one person at the entrance hall would have sufficed. There's no reason a player would listen to a guard telling them they can't go upstairs; not after having played the first few missions already.
2. The interaction/dialogue to have Lady Boyle's friend reveal her dress colour should have been more difficult to get, or at least more involved than just getting the friend a drink.
3. The alternate, non-lethal solution should have been more hidden.
4. There should have been a side mission, possibly for Granny Rags. She should have asked you to steal something from Boyle's mansion in return for another gift.
5. Perhaps if you wanted to stealth your way through, but also kill the Boyle, there should have been an insider that smuggled your weapons in, which you'd have to retrieve from them.
There were so many things that could have been done with that mission. It could have been amazing. As it is, it looks pretty, and I loved the change in pace, and I liked coming across tallboys for the first time (they're quite challenging to hide from, if you don't get up above them), and I liked how you could interact with people, but it just felt undercooked from an actual gameplay perspective.
It could have been better! Much better!
It's still a really good game in general. It just would have benefited so much from some extra finesse in some areas ...