I've seen 'em. I like 'em.
Some of them are kind of weak though. For example, the Abe Lincoln versus Chuck Norris one didn't really do justice to either of them. I did like the Romney versus Obama one though. Mr T versus Mr Rogers was hilarious, IMO.
I showed those videos to my niece and she loves them. I think the "beats" are well done but I'm not a "rap expert" so maybe they're horrible to connoisseurs of the genre, but they're funny nonetheless.
Personally, I don't listen to rap, hip-hop, or any of those genres. They're not very appealing to me. These videos are the exception though.
I thought the Steve Jobs versus Bill Gates one was kind of cheesy but I was somewhat impressed with the amount of knowledge they had on the matter. I didn't check to see whether they knew any of that beforehand, they did research, or just used someone else to fill them in on subjects.
Gregory House versus Sherlock Holmes.
Clint Eastwood versus John Wayne.
Batman versus Superman.
John Carmack versus Notch.
(Granted with Carmack versus Notch the winner would be Carmack if the subject were programming. So the subject would be games with Carmack representing id Software and Notch representing Mojang, obviously.)
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“I'm going to punch DXGI in the face. Repeatedly.” ~Aras Pranckevicius