Lots of regrets, but that's the industry-wide trend of making wannabe-iPhones for tweens rather than to keep making phones that are satisfying for business professionals. At least the 5x isn't made out of metal (which blocks every kind of signal there is) like the other phone-as jewelry (rather than phone-as-functionality) phones that manufacturers want to insult consumers with.
Pros: I can use Google Fi. Pure Android that's not bloated down by manufacturers or carriers.
Cons: Coming from a Galaxy S5, I no longer have an OLED display, I have no more memory than my 2 year old phone had, I have no more storage than my 2 year old phone had. I no longer have the ability to swap out my "personal life" storage (on Micro SD) for a "work/travel" micro SD. I no longer have water resistance, which rules out carrying my phone as a camera on snowboarding and kayaking trips. I no longer have wireless charging (and HATE having uncoiled wires dangling across my desk, dresser, and car interior - I'm past "college dorm" years!). I no longer have the ability to pop in a fresh battery after a 5am flight, heavy navigation at a client's city, heavy calling and messaging to the home office, heavy entertainment use while waiting at airports and eating at restaurants, etc... I have to pack and carry around a Rube-Goldberg "battery on a dongle", and a cord - embarrassing carrying it, embarrassing juggling it in almost any context. It's even slightly larger than my S5 was, which is an issue for a man who carries a phone in his front pocket. It particularly makes motorcycle riding uncomfortable in many pants whose pockets aren't very deep, as it pokes you in the hip. Let's not forget to recognize that the more powerful phone I really want is the impractically large one - the size forced this purchase of the 5x.
It really is cheapened, featureless design all around - but such is the industry trend that nothing out there was even a sideways upgrade for my Galaxy S5. So - "Oh well, might as well try out Google Fi" as at least a redeeming quality.
Other than that, I wouldn't call it "regret" as that would imply there were good alternative choices.