Honestly, yeah... Might end up being quite a mess, really.

• Wiemar Germany was never going to be a stable, peaceful, long-lasting country. With economic issues and resent for the treaties enforced on them after the end of WWI, it was a mess and a huge source of potential issues. Something awful was sure to come out of it sooner or later.

• Without the example of Nazi Germany to be against, the rest of the world might not have united against fascism as much, leading to the more prominent rise of fascism in other places.

• Without (European*) WWII, Europe might never have become as united as it is now. Post-WWII was kind of the tipping point where the major European powers finally decided that going to war with each other was unacceptable and unthinkable. And uniting together to fight the Nazis solidified alliances and feelings of mutual support between a lot of European countries. Without that, who knows -- we might have ended up having several more major European wars.

• And then there's the technological impact. Obviously, Hitler himself wasn't directly involved in developing these important new technologies, but would they have been developed as soon or at all if it wasn't for Nazi Germany, their war effort, and the Allies' counter-effort? Jet aircraft, rocketry, radar, computers, nuclear power/weapons ... much of the development of those was either greatly accelerated by the Nazis or greatly accelerated by the Allies in their attempt to keep up with and defeat the Nazis. Who knows what the course of development for technologies like those might look like if WWII hadn't happened.

*WWII in the Pacific with Japan probably would have happened much the same, regardless of whether Hitler was alive or not. Though in that case, it might not be called a 'world' war anymore. Maybe the 'War of Japan' or 'Pacific War' or something.