Lumia 900 was an OK product in the beginning. I was excited when I first bought my Lumia 900. However, it was a vanilla WP7.5 product with some extras like Nokia Drive--you could not even store your favorites destinations in Nokia Drive. However, it served a purpose by meeting my basic navigation needs. I paid only $50 for Lumia 900 and then Nokia gave me $100 back for a small bug--I got it for -$50 :-)
Interestingly lot of crticisms started when MS announced WP8 and declared that WP7.5 will not be upgradable to WP8--instead will get update 7.8.
Ironically, Nokia announced several new features and updates for Lumia 900 since then. We got:
Camera Extras-Smart Group Shot, Action Shot, Panorama, Self-Timer
Major update to Nokia Drive: Now you can have your favorite destination---the most intersting improvement was "Commute"--you can progarm your daily commute giving the time ofthe commute and destination say your office. The algorithm in the phone will tell you your commute time based on the traffic information so that you can leave early if needed.
Nokia Transit if you like public transport.
Major update to Nokia Map--you can upload photos.
Nokia Lens--very cool feature
Nokia Music--free music service--you can listen to free music--also you can purchase a song if you like the song that is being played.
Flip-to-Silence
DLNA--stream your photo, video to your DLNA enabled TV
and several other cool features.
Thu all talks about non-upgradability to WP8 is an opportunity for a smart customer--you can get a very advaned smartphone with LTE, Great Screen and bunch of features ( available onnu on high-end phones) for free.