それにしては details

Examples

for that — the previous statement is treated as a standard, and what follows overshoots or falls short of it

初はじめて作つくったって言いってたよね。それにしては、うまくできてるじゃん。

hajimete tsukuttatte itteta yo ne. sore ni shite wa, umaku dekiteru jan.

You said this was your first try, right? For a first try, it's come out well. casual

彼かれはもう十年じゅうねんも日本にほんに住すんでいる。それにしては、漢字かんじがなかなか読よめない。

kare wa mou juunen mo nihon ni sunde iru. sore ni shite wa, kanji ga nakanaka yomenai.

He's been living in Japan ten years now. For all that, he still struggles to read kanji. neutral

大おおがかりな宣伝せんでんをしたと伺うかがっております。それにしては、来場者らいじょうしゃが少すくないようです。

oogakari na senden o shita to ukagatte orimasu. sore ni shite wa, raijousha ga sukunai you desu.

I understand a large advertising push was made. For that, the turnout seems low. formal

にしては
にしては keeps its yardstick inside the same sentence, on a noun or a clause (初はじめてにしてはうまい); それにしては moves the yardstick out to the whole sentence before it, so it needs a proposition already stated and cannot open a conversation.

それに対して
Four connectives open on それに and what follows decides — bare それに simply adds another point, それに対たいして either sets the new sentence against the old one or answers it, それにしても grants the old one and asserts anyway, それにしては measures against it and reports a shortfall.
それにしても
One particle apart, opposite verdicts — それにしては measures what follows against the premise and reports a MISMATCH, それにしても accepts the premise and asserts what holds anyway; read one for the other and the sentence's conclusion inverts.