The Soviets loved the P-39 Airacobra.
Five of the 10 highest scoring Soviets aces logged the majority of their kills in P-39s. Grigoriy Rechkalov scored 44 victories in Airacobras. Pokryshkin scored 47 of his 59 victories in P-39s, making him the highest scoring P-39 fighter pilot of any nation, and the highest scoring Allied fighter pilot using an American fighter.
https://en.wikipedia.org/wiki/Bell_P-39_Airacobra
P-39 had excellent low altitude performance but was terrible at high altitude. Since most air combat on the Eastern Front was at low - medium altitude, the Soviets were fine with the P-39's operational limitations.
My recollection is the Soviets liked the P-39 as a hard hitting ground attack aircraft that could fight its way out of trouble unlike the Il-2.