The "purges" of which you speak are more correctly called proscriptions, because they didn't involve just wantonly killing political enemies, but were (at least technically) a legal punishment. Under the punishment of proscription the name of an enemy of the state was publicly posted. The result was that the proscribed immediately lost status as a citizen and lost all rights to possessions and property, which was promptly seized by the state. The proscribed had to leave Italy immediately, and could be killed by anyone who saw them. The families of the proscribed could not inherit property, their wives could not remarry, and anyone who helped the state track them down would receive substantial awards, which often turned many families against relatives who had been proscribed. Sulla's proscriptions were unprecedented in their scale--the OCD lists 520 people as being proscribed as political enemies. There were no proscriptions before Sulla, at least no large ones targeting all political enemies in general.

Sulla's proscriptions, however, were not the first massacre of political enemies. The proscriptions were at least in part retribution for the massacres that the Marians had committed in 87 and 82, but those had been largely illegal acts of unadulterated violence. The proscriptions were organized, massive, and terrifying. The Marians had at least only murdered their political enemies--Sulla included many wealthy, but politically irrelevant, families on his list, in order to use their confiscated estates to replenish the severely depleted treasury. The panic and terror that Sulla's proscriptions caused is pretty well-documented--even though only about 500 people were targeted, it could be anybody, regardless of political affiliation. And proscription was a terrifying punishment. Whereas the Marians had just gone out and arrested all their enemies and then massacred them, the proscriptions could tear entire families apart, turn all your friends and neighbors against you, and doom your children (the sons and grandsons of the proscribed were not allowed to hold political office or engage in political activity until Caesar's consulshipdictatorship lifted the ban). And even if you escaped death it meant a life of exile, and though many of the proscribed who escaped were later pardoned the damage was often done, especially with regards to property loss.

It was a scary time. We have lots of references to the total hysteria that swept through Italy. Nobody knew when he might be proscribed and taken out by gangs of Sullan thugs in the night. The state provided generous rewards for those who assisted in hunting down the proscribed, and threatened punishments for those who knew something but wouldn't help. People like Crassus (who sided with Sulla and started snatching the property of the proscribed for himself), Catiline (who, according to Cicero, tortured his brother-in-law to death and brought his head to Sulla), and Pompey (described by contemporaries as the "creature of Sulla") were quick to capitalize on the spirit of the time and jumped in. It was pretty nasty, and it remained in the Roman consciousness for some time.

It's notable that even supporters of Sulla's preferred to sweep the proscriptions under the rug. A fairly large portion of the senatorial class supported Sulla's reforms, particularly the hamstringing of the tribune of the plebs and the reduced political opportunities for equestrians. Others, like Cicero, disapproved of much of Sulla's work but supported it inthe hope of stability and Cicero's idea of concordia ordinum. And of course Sulla's remaining enemies were livid, and in any case much of Sulla's work was undone or modified immediately after his death. Support or opposition to Sulla's constitution was a big rhetorical point in late Republican politics, and Sulla's constitution or laws passed under Sulla are constantly being brought up, either to be torn down rhetorically or defended. But nobody wanted to be reminded of the proscriptions, you can tell when Cicero brings them up in his speeches that it was an uncomfortable topic for everybody. Even when he accuses enemies of participating in the proscriptions he refuses to dwell on it and moves on as quickly as possible, as if to remind people, "Yep, that happened, let's not talk about that." And the possibility of the use of proscriptions in the future always loomed over the state--Caesar was praised to no end for not starting up a second wave when he took over.

Were they the worst? They were certainly the most damaging to the spirit of the Roman people. Sulla's proscriptions persisted in memory well into the Principate, and they were always one of those nasty incidents that everybody just wants forgotten. But they weren't the only political massacres--we've already seen Marius', which were quite frenzied and bloodlusty (is that a word?)--nor were they the only proscriptions, or even the largest. Before Philippi the Triumvirs, low on funds and surrounded by enemies, resorted to proscription. We know that around 300 senators and equestrians were listed, and the total of the lists were probably at least equal to Sulla's. But the Triumvirs were more concerned with money than killing people, and a lot of the proscribed were able to escape and were later pardoned. The Triumvirs, though, did proscribe kind of indiscriminately--alongside obvious enemies like Cicero the lists included Quintus Cicero (Cicero's brother and a devout Caesarian, who had served as Caesar's legate in Gaul), Lucius Caesar (Caesar's cousin and an important Caesarian), and Lepidus' own brother! But Sulla's proscriptions were still thought of as being much nastier, and were probably a lot bloodier. Was the nastiness exaggerated? Mmmm, almost certainly, after all Sulla didn't make himself particularly popular with anybody, even those that supported his laws. But it certainly was a nasty time, and the Roman people appear to have been genuinely terrified in a way that that had not been during Marius' massacres or after Sulla's proscriptions that the state might make a deliberate, well-organized roundup of political enemies and basically anyone that they didn't like.

EDIT: So, /u/LegalAction has correctly pointed out that I kinda confused myself a little bit :3 My own opinion, and the opinion of most scholars, is that Sulla's proscriptions were really rather tame compared to those of the Triumvirs, at least in terms of the number of people proscribed. We don't have many reports of the kind of weird shit that was going on during Sulla's proscriptions as happening during the Triumvirs' but that may well be simply because of the shock that Sulla's proscriptions had on people (and also maybe because the Triumvirs organized theirs a lot better, Sulla's proscriptions were rather notoriously corrupt, with guys being put on the list by Sulla's lackeys for personal reasons or because they wanted their property). When speaking of how nasty or not nasty Sulla's proscriptions were the effect of the proscriptions in the Roman consciousness should be kept in mind--for people like Cicero this was the first time something like this had been done, and it was undoubtedly exaggerated in scope compared to later proscriptions