10/10 suggests, to me, a certain agelessness and quality throughout - and that's somewhat subjective, because it all hangs on how something hits you. I've only really ever had one game that achieved this - RE4.
Every single time I play, I'm having fun and feeling tense the entire time. There are no lulls or slogs that feel annoying or cumbersome. There are so many rooms you walk in and go "oh, fuck, this place again" and yet they still manage to be nail-biting, ass-clenching good times through and through. My resources are always just barely enough to scrape by - wrapped up in a hokey, goofy story that doesn't outstay its welcome and introduces hilariously campy characters. With fun extra modes and incentives to play the game over again.
It isn't even necessarily the type of game that I most adore or most want to view as a 10/10, but it's the only game I can think of like this. Dark Souls 1 from start to O&S is probably also a 10/10 experience, but immediately after that point it disintegrates into a boring slog. New Vegas' combat gets incredibly stale and boring, and the world exploration begins to feel uninteresting and repetitive. Plenty of FPSes have levels that you'll grit and bear and just rush through because they're annoying, not because they're tense. The RE2remake's minute-to-minute gameplay was fucking genius, but then it had the goddamn shit-tier boss fights.