Holy shit, the menu was so bad. Ads and other shit everywhere. Cluttered and inconsistent such that it was tricky to find anything—I still have one, and still play games on it sometimes, as recently as last week, but even today don't feel like I have a good mental model for the menu layout and functions, everything just feels randomly strewn about, that even goes for the in-game pop-up system menu.
And yes, it's noticeably laggy.
I've not been happy with the direction of the PS4 and PS5 menus, but despite a ton of shitting-up compared with the sublimely-snappy-and-simple PS3 menu, they're still not that bad—and at least they have the horsepower to run the webshit Playstation Store without constantly running out of memory and refreshing, or crashing, or taking comically long to load a page. You'd think they'd prioritize a great store experience to get you to spend more money, but on the PS3, you'd be wrong. But anyway, point is the 360 menu is so bad that years of making Playstation menus worse hasn't been enough to catch up with its awfulness.
Haven't seen the XBone menu yet. Hope it's better.