I've had an early-version "flat" Airport Extreme (that was a hand-me-down!) running for going on seven years with nary a hiccup. Fine equipment.
BUT… I wouldn't consider buying an Airport Extreme today.
Of course the old "Apple user-friendliness" is still there, but Apple has disbanded the development team and no updates to it seem to be in the offing. I'll -guess- that it will continue to be supported through two or possibly three more iterations of the Mac OS, but at some point it's going to get relegated to the "obsolete" equipment category by Apple. Since they do that after about 6 years, the "current" AE is already two-thirds of the way towards Apple-labeled "obsolescence".
If you need a new wireless/router, I'd suggest you take a month or two and seriously investigate the various "mesh" solutions on the market, such as Orbi (Netgear), Velop (Linksys), eero, google wifi, Amplifi (Ubiquity), luma, etc.
All the more so if you have more than 1,500 sq. ft. and more than one floor that needs coverage...
agree. if extended coverage is an issue then the mesh routers is the way to go. we almost bought an orbi when we moved to a bigger place -- found out our airport extreme vertical version provided good coverage.
is the latest airport extreme still worth buying? would say yes if you want unique features like time capsule support and don't have a huge house
Unless you want 802.11ac, the 4th gen AEBS should continue to work fine for you. I'm using the same one myself, having upgraded to it a few years ago from a second gen. I don't think Apple is putting much effort into these anymore, however, so unless you have some reason to prefer an Apple router (e.g., AirDisk, Time Machine via the USB port--only officially supported on the 6th gen, BTW--or the desire for Server.app to be able to manage some settings on your router automatically), I'm not even sure I'd consider it anymore. Additionally, with the latest generations, you'd actually lose some functionality in that AirPort Utility 5 doesn't support them, only AirPort Utility 6. If you don't plan on changing many settings it won't matter much to you, but many things were easier in v5, and v6 downright eliminated some (albeit probably less used) functionality that I find useful (e.g., transmit power and the ability to see more than two DHCP reservations at the same time).
If I ever replace my AEBS 4, it's probably going to be with something non-Apple, probably something I can load an open firmware onto (though 802.11n routers that support that seem to be rare, to say nothing of 802.11ac). EDIT: Actually, DD-WRT-compatible routers are easier to find than I thought, including the Linksys WRT AC1200, which is probably what I'd buy if I had to get a new one right now. A bit cheaper than Apple's options to boot.