I never had an S5 but I had an S3A...
...and I used it loads. In fact, I'd probably still be making use of it today if it wasn't hamstrung by its unusual protocols.
* The word processor was a delight. Simple yet effective. There have been many times I've waited for dentists, doctors, trains, and such and just knocked off a document. The keyboard is small but ergonomic so typing things isn't a hassle. It isn't as capable as Google Docs, obviously, but it could run rings around every single feature phone word processor I've seen and even bested early versions of GDocs.
* The word processor can "print" to a file. I don't remember the specifics now (it's been a decade), but it was something like it could "print" to a LaserJet and write the results to a file. Imported to a PC and passed through Ghostscript, this created the smallest damn PDFs I've ever seen. It was great for times when you just wanted a text document with no frills (but basic formatting and effects).
* The spreadsheet was simplistic but capable enough for basic tasks, as was the database. But when these really came alive is when you learned a bit of OPL and could roll your own programs.
* OPL. A simple BASIC-like way to build applications for the organiser. I wrote my own bank account management software, it was actually not that hard. I also did some stuff like resistor colour code calculator, hex calculator, and the like. So when I wanted to know something, I could open my S3a and look it up. This is something desperately missing from Android phones. Sure, you can write fully fledged apps, with a complete SDK....but if you just want to put together something simple for your own use, it doesn't exist (that I know of).
* Battery life. Okay, it's a slightly sub-8MHz x86 clone on some custom silicon with aggressive power management techniques, but it was not only pretty impressive to have a hand-held device with the power of the early XT back then, but for it to run for weeks on two AAs? Whoa. I don't know about you, but I charge my smartphone every night...
* Stability. In normal use and not trying nutjob stuff in OPL to mess with the processes, the S3a NEVER crashed. I guess there might have been bugs, but I never had the word processor randomly did on me. I never had the thing inexplicably reboot itself or just shut down (it did, but that turned out to be a dodgy battery connector).
* About the only thing I could complain about was the weird flash memory card that would just append data to the end of the used space until the card was full. Then you'd need to copy the data off and reformat it. That said, it was possible to dump "constant" information and apps onto the flash and flip the write protect switch, using the internal memory or RAM pack as random access storage.
This, I should reiterate, is talking about the S3a. I can only imagine the S5 is all of that and more. They were really incredible machines and just imagine what could be possible if that mentality was applied to modern hardware? I think the thing that I miss most is that nothing at all really works entirely "out of the box" any more. Okay, it isn't difficult to go grab some app or other, but the point is that all these things are third party add-ons in varying degrees of usefulness and cloud-associativity.