I just got my 830 last week. So far the problems I have had are:
• camera won't always zoom
• very very poor reception compared to my n900
• poor battery, not even a full day, taking photos with flash, a couple of calls and some web browsing
• windows Facebook app keeps closing so I have uninstalled it
• web page Facebook doesn't for on the screen until I go into a post and then back to the homepage
• intermittent scrolling lag
• backlight intermittently dulls and brightens
• jagged movement with scrolling
• very often have the loading screen, sometime pages won't load
• very often have the resuming screen
• gets hit quickly
The only things I like are the swipe function and the phones size.
Is my phone a lemon or am I expecting too much or doing something wrong?
1 - Are you swiping up and down with your finger?
2 - Could be a variety of reasons. n900 was an amazing phone, so would not be surprised if it has better reception. Try getting a new SIM.
3 - Yeah, get used to it ... Nokias Maemo/Symbian devices seemed to have much better battery life despite smaller capacity.
4 - Something could be wrong with authentication, not a common issue. Try reinstall/wipe, idk ...
5 - S400 SoC is not that great really, needs some optimization from Microsoft.
6 - That is normal, ambient light sensor. Set fixed brightness, or keep your finger off the sensor
7 - Either a bad app or a really long list.
Universal apps are going to have this issue more frequently, because there are more shoddy developers in this world than there are good ones.
8 - Yeah, this is not n900. Say goodbye to multitasking? Hopefully Windows 10 will fix this
9 - Windows 10 or fail
10 - Wipe your phone, disable some background apps. Lags will occur if the phone gets too hot and has to throttle.
You are expecting a Nokia phone and getting a Lumia. That is why you are not happy. You cannot be "happy" unless your expectations have been exceeded.
n900 is a completely different platform, with different philosophies in mind. Can list more than a dozen features that Windows Phone 8.1 is lacking that Windows Mobile 6 had.
You could play the wait game like many of us are now, or you can find a platform that meets and exceeds your expectations. Honestly, I would think you would be happier with a Z3/compact since you are coming from a n900.
Good luck
EDIT: Spoiler Alert ~ Better lower your exceptions and understand the limits of today's smartphones.