In the interest of quantification.
If you've only played Basic, there are 340 possible levels to experience Basic D&D: 4 races * 4 classes * 20 levels each + 20 levels of DMing.
If you're playing with the PHB, there are 80 classes (including subclasses), 28 races, and 20 levels + 20 levels of DMing for 2,260 total levels.
I'm simplifying the DMing side - I could also figure out how many monsters it takes to get enough XP to get a level and compare that against the total number of different monsters in the MM, but I don't know a reliable way to get that first number over 20 levels (happy to accept help from fellow quants, though!

).
So take the number of levels you've played, put it over the total possible for the style you're playing in and figure your percentage.
For my Monday group, for instance, we're level 6, so we've each had 1 class for 6 levels, and 1 DM, and we're using the PHB, so we've each (including the DM) experienced roughly 0.2% of the content of 5e so far personally. And with 5 regular players + 1 DM, that'd be about 1.2% of the game as a group (minus the people who haven't been there for the whole thing).
So, what percentage of the game's experience have you actually played through yourself? What about your group as a whole?
This calculation is part of what reminds me that "more content" is rapidly diminishing returns...I haven't experienced even 1% of the
current content of the game! And that's probably true even when you add all my separate groups together!
How about you?