I have a Lumia 620. I picked it up after I broke my Nexus 4 (I loved the Nexus but the screen cracked from a 1 foot drop!) and needed a smart-ish phone asap but couldn't justify spending £330 on the Nexus 5 at the time so picked up the 620 as the reviews said it was ok and I had a play with it in store and it seemed good enough.
Anyway I have had the 620 for 4 or 5 months now. Physically the phone is pretty lovely. Solid Nokia build and all round very good. My only issue with the physical bit of the phone is the touch screen plays up in cold weather which I have never had before. The real let down for me is Windows Phone 8. It isn't bad but it also isn't good. Some things about WP are lovely such as the beautiful font rendering. I was/am really impressed with the fonts on WP8 (and Windows 8). The 620 has a low resolution but still managed to look really nice when it comes to font rendering. Apple have caught up with iOS7 though which leaves Android lagging behind in the font department (same is true for Chrome with its crappy font rendering).
My biggest issues with WP8 though is that it is just way too limited. I know iOS is limited too but WP is just horrible. I mean I can't even drag the scrubber in the music app to seek in a song! There is no way to disable the animations which get very tiring to watch. The app eco-system is still **** poor. There are dozens of apps but nothing of great quality. There are horrible UI inconsistencies, especially with apps such as some using coloured icons, some using Modern style with their own colour and some that dynamically adjust their tile colour with the theme. They should have taken the Apple approach and enforce a strict icon design as it makes the UI look ugly with manky icons and stand out colours for the odd app when everything else keeps to the same style.
It is also missing several built in such as a stopwatch and timer. There is a free Microsoft Weather app in the store but it doesn't come on the phone (why?!).
It badly needs some kind of quick settings page for things like wifi, alarms, etc. I know it is coming in 8.1 but it really should have come with 8.
YouTube is just awful. The best you can get on WP is MetroTube which still sucks.
Having Office built in seemed really nice but in reality it is crap. Compatibility sucks. I got much better compatibility with Polaris Office on my Nexus. OneNote is nice (I love a good note app on my phone) though. Also no built in PDF reader is poor.
The settings "app" (or whatever you want to call it) is just a big mess and needs to be reorganised. iOS 6 had a similar issue which Apple have mostly addressed in iOS 7.
Now for some of the things I do really like about WP8. Data Sense is very nice to have. Visually it is great and is very helpful. There needs to be a Battery Sense app as well so I know what is killing the battery! (btw the battery on the 620 is horrible, it often dies in the night and I have no idea why!). The keyboard is really, really nice. Not perfect but very good for a stock keyboard. I can imagine it being even better on a slightly wider screen. Live tiles are great. I prefer them to widgets on Android by a long shot. The three different tile sizes is also really nice. The messaging (SMS) app is cool how it integrates everything into one stream of communications with easy switching. The 30 stage volume up/down is amazing. I wish iOS and Android had such fine grain controls for the volume. The music app has great sound quality not just for the price but for all smartphones I have owned (which is a lot). Fonts as I already mentioned are amazing so needs to be mentioned twice.
Anyway that should be enough for now. I am sure there are more things both good and bad but I need to do some housework
Some valid points there. I'm hoping Windows Phone 8.1 is a sufficient upgrade to eliminate most problems.