I haven't been on these forums in a while (been getting busier with my hobby of making music :grin
but I thought I'd come back and give my thoughts since I've had my 830 for a month now.
So, my 920 had been slowly dying and finally gave up one day and I was stuck on AT&T, so I had limited choices. I tried the 1520 and didn't like the size, the 635 seemed too underpowered for me, which left it between the 830 and the M8. I really couldn't decide which to get because the 830 has a little bit more powerful camera and is Nokia, which pretty much guarantees good support, but the M8 has that fancy 801 SoC and a faster camera until the 830 get the actual Denim update (right now it just has the update that says it's Denim but doesn't actually enable the new camera tricks yet). After messing around with them both in store, I didn't like either the on-screen buttons or the general feel in hand of the M8 and the 830 felt amazing. The M8 kinda disappeared in my hand and I felt like I couldn't hold on to it, and the 830 definitely felt like I was holding a very nicely designed phone. Maybe I'm just used to holding the massive 920. The 830 really does feel amazing, though.
Performanc-wise, the 830 is nothing to write home about. Within receiving the phone, I almost immediately loaded it down with all my apps and music and filled out my start screen (two screens worth of apps with 8 folders). It did take a noticeable hit in fluidity from this, but seems to run fine most of the time. I haven't noticed the stutter from scrolling up on the start screen due to the Cortana tile like some people have complained about, but I do get a resuming screen after pressing the start button fairly often, even if I empty my start screen to be bare-bones, which I don't understand. Switching between apps usually conjures up a resuming screen, too, but only for up to a second with the exception of MixRadio and Lumia Camera (Classic) getting longer resuming times. I'm sure that I don't have a very friendly set up to the processor, and I tend to use my phone sporadically and erratically, which I'm sure doesn't help, either. If I'm kind to it, it runs buttery smooth.
Another bug I've seen people talk about a lot is with the back button not being responsive. I have had this happen, but only once. I think. For the most part, I just miss the back button with my thumb because It's a little farther in from the edge of the phone than I'm used to.
The screen is very nice and I love the size of it. That extra .5" diagonal from the 920 is refreshing. It isn't stunning resolution, but I wouldn't bet you'd notice the pixels, either, unless you look closely, and animations flow nicely. the glass is kind of thin, and you can kinda get that wavy LCD effect on the edges of the display when you press hard enough. I can't comment on color reproduction.
The build quality of this phone is nothing less than what is to be expected as the last phone to carry the Nokia badge. The back cover fits flush with the metal edges and the little lip around the camera provides some decent protection to the oversized piece of glass. I've dropped it a couple times on concrete (and linoleum covered concrete), and there is zero visible damage. What I can't get over, though, is how nice this phone feels in the hand. I got to hold the 930 and some other phones in the MSFT store, and this feels the best, IMO. Even the buttons feel very nice and provide excellent tactile feedback. The first of the two stages of the shutter button is very shallow, but I've become really accustomed to this. It's almost like you just set your finger on the button and the phone knows your finger is there, ready to take a picture, and it focuses the camera.
I won't comment on camera speed because I'm not running Lumia Camera v.5 yet, but the quality is excellent both in pictures and video. I tested out the mics at the ice rink and it picked up that distinctive hockey skate sound in pristine quality (for a phone... starting to get close to a low end studio mic that I'm used to, but not quite there yet). I won't really say much about the speakers, either. They're phone speakers. Don't expect much out of them, but they play notification sounds loud and clear and that's all they need to do. The earpiece is really good, though, and I can hear the people on the other end of the line really well, even in less than ideal environments (walking down Montlake Blvd in rainy Seattle during rush hour with the phone in my hood) and people said they can hear me really well, too. Much better than on my 920.
This phone is generally considered a sidegrade from the 920, but I don't think I agree. It's an upgrade. A slight one, but still an upgrade. You get better battery life, an SD card slot, much better feel-in-hand, and a newer SoC without losing anything. It doesn't perform worse, it has all the same sensors and features (plus a few like miracast and surround sound recording). Sure, it isn't some amazing giant leap forward, but I don't quite understand how it's a sidegrade.
I could talk about this phone for days, so if there's anything else you'd like my opinion on, just let me know