Many people think that the God of the Old Testament was not merciful, yet his wrath was turned by through the pleading of prophets.
Most Christians look upon Christ as being more merciful that God the Father, since Christ died for our sins — total unconditional love for the Father and for us.
But I tend to think that the real joy comes through God the Holy Spirit.
Even though some people might think that about God’s actions in the OT, I don’t think that the muslims even try to portray their god as merciful.
I have found that the people who like to portray God in the OT as bad as Allah, generally have a bone to pick with God anyway, and it seems like they use that as an excuse to reject Him and justify it.