Do you think this opening is good for black.?
1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 dxc4 5.e4 b5

The main line begin 5.a4, it should answer your question...
Your question should be : do u think it is good for white?
I don't think there is a definite answer to this question.
e4 (known as Geller gambit) leads to double edged play and is quite fun.

It's not clear to me that white has enough compensation for the pawn or even a clear plan. I always play 5. a4 to prevent this line. Black can easily fianchetto the bishops and develop. If white ever plays e5 black has Nd5.
The white pawn breaks a4, b3 and e5 are always possible but it doesn't seem logical to me to play a pawn gambit only to spend energy getting the pawn back and even so it's not clear black would be worse.

The main line begin 5.a4, it should answer your question...
Your question should be : do u think it is good for white?
I don't think there is a definite answer to this question.
e4 (known as Geller gambit) leads to double edged play and is quite fun.
to poucin, what benefit to change the question? and no reason why "should" ask yours instead of theirs. the asker wants to know the item they asked...

Do you think this opening is good for black.?"
it seems good until "5 b5" because pawns can only move forward hence it is weak to move them forward in the "opening".

The main line begin 5.a4, it should answer your question...
Your question should be : do u think it is good for white?
I don't think there is a definite answer to this question.
e4 (known as Geller gambit) leads to double edged play and is quite fun.
to poucin, what benefit to change the question? and no reason why "should" ask yours instead of theirs. the asker wants to know the item they asked...
Because the question was not the good one.
If 5.e4 b5 is bad for black, it means 4...dxc4 bad for black, which should be a revolution in chess theory.
So I consider the real question being : is 5.e4 b5 good for white?
Which is more relevant to answer.
But anyway as I said, nobody really knows how to answer this question.
Do you Think this opening is good for black
?