好奇の視線と、若干の殺意のこもった視線・・・言うまでもなく居心地が悪いことこの上ない。

、・・・。

Curious looks and gazes laced with a hint of murder — needless to say, this place couldn't have been more uncomfortable.

Literal

Curiosity-[attributive-の] gaze [and-と], slightly murderous-intent [subject-が]-filled [attributive] gaze... needless-to-say comfort [subject-が] bad [thing-こと][nothing-beyond-この上ない].

Uncomfortable narration. 好奇の視線 ('gaze of curiosity') uses 好奇 ('curiosity') attributively. 若干の ('a small amount of, some, slight') is formal. 殺意のこもった ('filled with murderous intent') uses 込もる ('to be packed/filled with') in its attributive past form. 言うまでもなく ('needless to say'). 居心地が悪い ('uncomfortable,' literally 'the feeling of being-there is bad'). ~ことこの上ない intensifier.