It isn't and never was. I played it at the time and even as a teenager I thought it was unimpressive. I have never cared for stealth in games that are that linear. The boss battles are more annoying than inventive. The plot is like some kind of weird mish-mash between something more serious and American and Japanese anime eccentricities. The first time I played a metal gear solid with truly good gameplay was V because it dropped the overly scripted nature of the franchise. Kojima clearly wants to make movies but the young gamer audience was exactly the right target if you wanted people who wouldn't scrutinise the level of exposition in a game that still doesn't make sense. People who would celebrate an 18-hour game being 9 hours of cutscene. People who didn't know what a proper tone for a game was to have a problem with awkward tonal shifts.
Part of me envies people who were the right age or right mindset to enjoy this kind of thing, that might sound condescending but I really do think you have to be in a certain mindset to enjoy these games and the best evidence of that I seen is that the fans of this franchise think part 5 is the worst one which to me is so weird. I'm sitting here like finally a reason to use all these silly options finally a game that actually gives me a sandbox to play in where these things are actually useful. I'm playing metal gear solid 3 words giving me all these dumb camouflage options to get through 2 minutes of gameplay. all these silly tutorials that gave me none of them really mattered because the game played like a Michael Bay movie with small gameplay arenas sprinkled throughout that anyone could brute force their way through with enough patience or tenacity.
I feel like I'm on the outside looking in like the people who hate Half-Life 2, the difference between me and them being that one episode two went more open for the finale I thought it was amazing and was totally welcoming a more open world half life or even if it meant spacing out the cinematic nature of the game more. But the reception 5 receipt proved to me that the average metal gear solid fan was more interested in the absurd incomprehensible stories than the interesting game play systems and how they interact with the world. which again I don't totally get to me stealth just doesn't work if there's not enough different paths stealth is trial and error and there's only one way to do it it annoys me and bores me.
