To be honest, even Japanese Peace walker sales aren't that great all things considered imo. Konami really went out of their way to try and make it a game that would expand the MGS audience and appeal to the active PSP base (co-op, MoHun tie-in, etc) and it still seems like it's only sold to the same series faithful. Series sales comparisons...
- MGS1: 705k
- MGS2: 798k
- MGS3: 820k
- MGS4: 706k
- MGS5: 728k
...and with rereleases and budget reprints...
- MGS1: 905k
- MGS2: 1127k
- MGS3: 1118k
- MGS4: 853k
- MGS5: 728k