Just as the title says, was the persecution of Christians in the Roman Empire really as bad as it's made out to be, or has it been romanticized a bit? Were they actually hunted down and fed to lions in the Coliseum and things like that? Trying to solve a debate with someone, and I realize I don't really know the answer to this.
Depends on which period, ruler, and region you're asking about. One of the real problems with talking about the history of Rome in general is that it has a rather large history, with a huge number of emperors and regional authorities, who often have conflicting interests, motivations, influence, and penchant for violence against minority groups.
Christians in Roman civilization have run the gamut from persecuted minority, to a group of interest and conversation, to sanctioned religion, back to persecuted religion, to official religion and borderline majority, and every where in between depending on where, when and who. Heck, they don't even keep a single ethnicity, as there are converts from every end of the empire.
For what it's worth, we have primary documents from the early church that describe a number of early martyrdoms. Perhaps most famous of them (apart from the scriptures) is the Martyrdom of Sts. Perpetua and Felicity which you can access at: http://www.earlychurchtexts.com/main/perpetua/passio_of_perpetua_01.shtml
It's pretty serious stuff.
Christians were treated with varying degrees of tolerance and persecution from the moment Paul really got the following going in the early 1st century AD.
Since the First Jewish Revolt and the destruction of their Temple in Jerusalem, Vespasian demanded that all of the Jews in the empire pay a tax towards the reconstruction of the Temple of Jupiter in Rome, the ultimate slap to the face to the monotheistic Jews. Nerva lifted the tax from Christians when he was emperor because he saw them sufficiently different enough from the other sects. Trajan continued the lenient policy and essentially said in one of his letters that the Christians were to be treated equally under the law as pagans.
Sporadic bouts of Christian persecution would come up again and again depending on the emperor until Diocletian ascended to the purple in 284 AD. Following the prompting of Galerius, his junior colleague, he commissioned the last and greatest persecution which would last until 310 with Constantine and Licinius' Edict of Milan, which more or less legalized the religion.
Well, it was bad enough for people to believe Nero would be reincarnated as the Anti-Christ.
Edit: Probably best to have a source that isn't Wikepedia. Although I'm not sure if you'd consider biography.com much better of a source.