I must of got a perfect S5, have no lag, no vibrating speaker/buzz or whatever people are talking about, have iPhones still too. Some on xda had a lag of a couple seconds, no clue there, mine is just as responsive as my iPhones when using home button, switching screens, or multi. Flap on the charge port doesn't bother me at all, easy to take out, plus my S2 died in water so to me it's priceless (after being careful with that phone for so long lol). Plus this thing actually takes sweet pics and vid under water haha. First phone where I have no worries, go on the boat no worry, our dock no worry, pool with splashing or dogs running around or kids... no worry. I get why some don't like the feel of it, plastic isn't going to feel like metal, but it doesn't feel cheap either. Either way 99.9% of the population puts cases on their phones so your covering up that metal anyway, I put a Rearth Slim on mine which I love, and it's grippy/feels great.
Battery life is ridonculous on this phone even in heavy use, first phone I've had where I also have no worry about getting to a charger or being out and about. Plus worst case you can enable power save mode which will last hours upon hours even if your below 10%, haven't had to do that yet though lol but nice to keep in mind if I have too.
Not having root though does suck balls on AT&T. Pry be awhile before root is ever exploited on this version and even then will pry have no workaround of Knox trip. Just like the AT&T version of the S4, unless you got an early loki one, you were stuck with safestrap and tw based roms barely tweaked (at least nothing like the tw roms on my S2)