Uhm... Where have you read that? Strictly speaking, Caesar was a war criminal in more than one aspect, but I can't recall ever reading about him doing that. Crassus did, however.

Caesar is remembered today in large parts because of Shakespeare, who took a liking to him. But more to the point, because he was an outstanding general, a decent politician and a major figure in the turbulent years of 1st century BCE Rome. I wouldn't say that he's one of the only rulers who is remembered either, but he's without doubt one of the most well-known.

If you're interested in learning more about the man I'd suggest you pick up Adrian Goldsworthy's Caesar: Life of a Colossus, as well as a have a read through of Caesar's own De Bello Gallico, available online.

Why is Caesar the only ruler still remembered today?

Well he's certainly not the only ruler remembered today, but to answer your question he profoundly changed the course of Rome after he claimed power (although to be fair Augustus did far more than Julius Caesar did to build the empire and he also laid a lot of groundwork in maintaining Caesar's memory).

He's remembered because he's a fascinating figure in history and the historical record of his life is (roughly speaking) quite robust. Although many primary sources have been lost there are still many contemporaneous sources of his life which paint a picture of a fascinating man.

All I've read about Caesar suggests that he was a cruel dictator.

Where are you reading this? Caesar was (as Romans go) fairly mild. For example he forgave most of the Senators who warred against him (after he illegally claimed control and declared himself dictator for life). In fact, many of the reforms Caesar enacted were quite populist and benefited the regular citizens of Rome more than the oligarchy. He was rather cruel (by today's standards) to his non-Roman enemies, but compared to other Romans he was quite mild.

I've read that as a punishment he used to crucify a percentage of the legion from which a bad apple did something wrong.

Where have you read this? I've never read this about Julius Caesar. Do you mean another empower who took the "Caesar" name?

This sounds like the practice of decimation, where a legion was reduced by one tenth as a punishment. I don't think Caesar practiced this (I could be wrong) although Roman generals both in the Republican era and Imperial era practiced it from time to time. It was a little unusual but not unheard of. Also crucifixion wasn't often used, rather the legionnaires who got to love were forced to kill the 10th man by beating him to death with a stick.

I'm wondering what your sources are for this?

Also, who exactly reveres Caesar? He's studied as a fascinating figure in history but I don't know that living people today "revere" him.