Depends totally on what is expected of it... If people expected a new IP like Z+W to sell "well" from the beginning they were not tuned in.
There is no statistical number a game has to sell to be a success. If the next main Pokemon only sells 8 million WW lifetime it will be considered a total flop, wheras If something like Z+W approaches 400-500k it is a massive success.
In monetary terms then you could argue that a game needs to be profitable to be a success, but the sales level a game needs to be profitable is different for each game too.... Something like MGS4 that costs tens of millions to produce and market may never turn profit even with 2 million sales, wheras something like Rayman Raving Rabbids was probably profitable with only 100-200k sales.
