For the Winter War, they got 9% of Finland's territory and put a damn naval base up in Finnish territory just like we got Guantanamo, and while Soviet casualties were high, Finland's casualties amounted to about a fifth of their entire military strength. Already not a good sign.
Then during the Continuation War, Finland lost even more troops (about a THIRD of their total strength), had to cede more territory to the USSR, pay the USSR reparations, and admit that they were a Nazi ally...which then forced Finland to fight a third war, in a row, against the Reich.
This still doesn't prove the USSR "sucks", if anything, it just proves that the USSR didn't have much of an issue sending its troops into a meat grinder.