Many people think the God of the OT seems to be different from the God of the NT. Mind you, I suspect many people who say that don't read the OT on a regular basis. Indeed, they may never have read the whole Bible cover to cover.
i) Atheist Christopher Hitchens thought the God of the NT was worse than the God of the OT because the NT accentuates eternal punishment, while the OT does not. Now, I think Hitchens overlooks some OT passages regarding eschatological judgment, but there's certainly much greater emphasis on eternal punishment in the NT. So one could turn the objection around. Although I don't think that's correct either way, it does present a different perspective.
ii) The OT is much longer than the NT. The OT is far more violent because Israel had to fight for her survival. You don't have the warfare narratives in the NT. But that's because the NT covers a different historical situation.
Likewise, because Israel was a nation-state, it had a penal code. That isn't pretty. What penal code is? That's a difference of genre, not theology.
By the same token, there's lots of criminality and palace intrigue in the OT. But that, again, is because the OT deals with the state of Israel. It's more political. Again, though, the difference is due to a different historical situation and focus.
In addition, there's far more coverage of pagan depravity in the OT. The difference is due to what the OT samples, and not different theology. The 1C Roman Empire had the same kinds of pagan depravity. But the NT rarely intersects with that.
iii) In the NT you have five historical narratives. Four concern the life of Christ. Those are narrowly focused on the public ministry of Christ. Plus a history of the nascent church. It's not like the patriarchal narratives, which shine a light on sinful individuals. Much less the historical books of the OT. The central character in the Gospels is a sinless individual.
There's nothing like the amount of violence you have in the OT, but that's deceptive. The 1C was tremendously violent. It's just that the historical focus of Matthew, Mark, Luke, and John leave out most of the warfare and criminality which raged in the Roman Empire.
You have lots of letters in the NT. These aren't historical narratives or penal codes, so the content is largely nonviolent. But that difference is due to genre, not theology.
Finally, you have Revelation, which is full of violent imagery. That's a lot like how some people stereotype of the OT.