Several more random thoughts:
--the whole phone feels very slim. The Optimus S felt more rugged/heavy/heavy-duty. I keep wondering if I am going to pull the phone out of my pocket to see the screen cracked because the area of glass is so large compared to the Optimus S and because the phone feels so slim (and potentially prone to flexing or being bent in half). Pulling the battery cover off the Optimus S revealed a solid metal frame that the whole phone seemed to be built around; pulling the cover off the Marquee reveals black plastic. So far, so good with the screen.
--Others have suggested good protectors/cases for the phone from eBay. I haven't bothered, because I really like how slim the phone is and I figure that the case won't do much good. The screen is already slightly recessed (the housing extends the slightest bit beyond the screen), so dropping on a flat surface should be ok, and if it's a super-rough surface like pavement on a street, then a case is unlikely to help anyway. The mirror finish on the back has gotten a little scuffed up, but that's the removable battery cover, which is available on eBay for about the same price as a protector. If mine gets too ugly from scuffs, I'll just buy a new one and snap it on.
--for the same reason, I love the fact that the battery cover covers both the back and most of the sides of the phone. If a drop results in a gouged/chunked-up corner, a new battery cover should address this as well.
--One of the things that made me chuck the Optimus S is that it was no longer charging reliably. Part of this may have been due to the flawed Android update that I never rolled back, but I believe it also had a physical hardware issue with an intermittent connection in the micro USB port -- the charger would usually work if I bent the cable in a certain way after attaching it, and then wrapping the cord around the phone to hold it in place. I don't know if this bad connection was the result of a connector that had gone bad, a loose solder connection, or just crud (dust etc) building up in the exposed connector, but the Marquee has a sliding cover for the USB connector that lets you keep the crud out.
--weirdly, the USB port is on the top of the phone -- I don't think I've seen another phone with it in this position, but it works fine, even if I'm listening to music on headphones in bed while it's charging.
--probably my biggest demand on the phone's resources comes if I'm listening to Google Listen, Stitcher, or some audio stored on the SD card and simultaneously playing Plants vs. Zombies. Both phones handle this without issues, but, on an advanced level where there's a whole lot of action going on, I THINK the graphics were smoother on the Optimus than they are on the Marquee. Not a huge surprise, considering that the new phone needs to deal with many more pixels, and if I recall correctly, doesn't the Optimus have a dedicated graphics chip that the Marquee lacks? At any rate, the Marquee works just fine at Plants vs Zombies PLUS mp3 decoding simultaneously, and Temple Run works fine too (never tried that one on my Optimus).
--I've noticed an increasing number of Apps on Amazon's Free App Of The Day that say, "Note: this app does not work with the LG Optimus". Not sure what the problem is (Flash, maybe?), and I don't think I've actually installed any of those apps, but I've never seen a "Note: this app does not work on the LG Marquee" message.
--the extra on-board memory is really nice. This was a constant concern with the Optimus, and I'd regularly clear out apps I wasn't using or clear the temporary files from the browser, but would still periodically get "memory low!" warnings on the Optimus. Yes, I moved the apps to SD whenever I could, but it was still so much of an issue that I eventually rooted the phone and installed software that utilized a partition of the SD card as virtual memory for the phone. I'm happy to say that I haven't had any memory issues on this phone.
--the camera is better on the Marquee than on the Optimus, but still not as good as my wife's iPhone 4 camera and nowhere near as good as my dedicated digital camera. I have discovered that the phone can be set so pressing the button pre-focuses and releasing the button activates the shutter, which has greatly improved laggy shutter issues, but it's still a tiny lens with a tiny sensor that works OK in broad daylight but suffers indoors.
--It's nice to see that many parts (screen, digitizer, back cover, volume buttons, USB port) are available on eBay, but it's also a little disconcerting, because it means that some people out there need those parts.
In particular, the current auction for digitizers shows that 24 were sold, which tells me that people are cracking the screens on these phones.