As you can see from Take-Two's quarterly report, the RDR series is doing very well. Recently, the number of copies sold of the second part reached 61 million.
In total, the games in the Red Dead Redemption series have sold 86 million copies worldwide. Most of the credit goes to the second part, but the first also does quite well if reports are to be believed. Take-Two called RDR2 "the second best-selling game in the US in the past six years." Let us remind you that recently it became known about a possible PC port of the first Red Dead Redemption, which Rockstar Games is working on.