SH: The Awakened was absolutely amazing, creepy as all hell, with an intricate plot and a nice variety of puzzle difficulties.
SH: Arsène Lupin / Nemesis was quite good, not as fun in terms of puzzles and story but you get a virtual, commented tour for free of most London tourist sites (National Gallery, ToL, British Museum).
SH: JtR was sort of an experiment in that it tried to make the game somewhat parallel an actual investigation - I think it was a lot more immersive, but it made the puzzles a lot less challenging or interesting. The historical work was actually top notch, all the leads and red herrings you chase were real events and people.
Oh, and yeah, the graphics are constantly horrible, but they've never made a point of spending much on them, and their customer base has never really cared much about it.
I'm frankly surprised they bothered to port this to the 360. As the confused comments here indicate, there doesn't seem to be a big audience for point-and-click, talk-heavy adventures there.