When I first played the original MGS, I was... I dunno, around 8-9 years old, so the twist that Master Miller was actually Liquid Snake all along naturally threw me off guard just a wee bit. But once I played through again a few years later, it kinda dawned on me that... Master Miller and Liquid Snake sound an awful lot like each other. I mean you can barely tell the difference! That wonderful son'bitch Cam Clarke is pretty much using the exact same voice for both. Even with knowledge that Master Miller is Liquid Snake, it still sounds like it would have been a kind of obvious twist to catch on for the older generation of players.
Though there's always the possibility that because of the general scarcity of voice acting--or rather good voice acting--during that era, maybe most assumed they had the same guy voice two characters for budget reasons? As such I'm highly curious to hear from the older video game players (and of course the more deductive pre-teens than I) about whether they can remember thinking to themselves ''Hey, Mike. Check this 'Master Miller' guy out. He's clearly Liquid Snake in disguise trying to manipulate Solid Snake into achieving his goals for him, and the real Master Miller is going to turn out to be dead this whole time! You'll see, now pass me a beer.''
Also I'm sure you all had a friend called Mike back then who you enjoyed drinking beers with. Because of course you did. Who didn't have a friend to drink beers with called Mike during the 90s? I should also mention that once Liquid starts getting extremely pushy when you call him up while you're waiting for those card keys to change temperature, it definitely starts to outright spell it out for you. Even my nose-picking 1998 self started to become a little suspicious. But I'm more so tying the predictability to the voice more than anything else.
Oh, btw spoilers lulz