What is Shakespeare's attitude towards war in Henry V ?
I think that overall, Shakespeare sees war as a glorious and patriotic endeavor in this play. After all, the climactic event in the play is the glorious and famous English victory over the French at Agincourt.
In the play, Henry is definitely the good guy -- he is an epic hero. So we should look at the words he speaks and think that these words reflect Shakespeare's ideas. Henry's speech about St. Crispin's day (Act IV, Scene 3, lines 20 and on) show war as a glorious thing. Henry says that people who are not here with them will think themselves accursed and will think they are less manly because they were not at Agincourt.
To me, this (among other things) shows that Shakespeare sees war as a glorious endeavor.