At the moment, this is what Interpersonal.SE looks like for a user who doesn't have an account and just followed a link from Google:
Now, I'm a frequent user of this site and I know that it isn't supposed to look like that. I get the joke and I'm OK with it, especially now, when it's relatively easy to switch back to a normal design.
But I don't think that it makes much sense to prank random visitors from Google. This joke won't work on them: from what they know Stack Exchange always has Comic Sans and unicorns all over the place. The popup message at the top is cryptic enough to confuse people even more.
May I suggest to disable the 90s look for non-logged-id users? Or, as an alternative, make it less intrusive (maybe even opt-in) for them.