So I have had/used the G900 since Friday, and all I can say with certainty is that I have not found phone nirvana yet.
Pros:
Size: Size is something that really bugs me about the flame. This is my 8th pda-phone (6035,Thera,XDA2,XDA2s,Jam,Jamin,Flame,G900) and having come from the Jam and Jamin I have come to learn the value of a smaller phone, so if you are accustom to the Jam,Wizard,Hermes size then the G900 is great.
http://www.flickr.com/photos/8476722@N04/969439618/
Keyboard: Of those previous phones none had a keyboard so I'm really comfortable without one, but having had a keyboard for only a couple of days I can honestly say that I would only do an email/sms now with it.
Bluetooth: As you would image bluetooth stays on when in suspend and the carkit is working great.
Battery: The battery is not GREAT, but its better then the Flame. From 2pm Saturday to 12pm Sun no charging doing 6 sms's, 1 call, (about 2 minutes) about 1/2 hour of video watching with bluetooth on the whole time it was at 60% battery. I don't think the flame would have even made it.
Cons:
Speed: Though the same processor family and both overclocking to a limit of 585, the G900 is MUCH slower then the Flame. Its actually VERY surprising, some times just clicking on the start menu will take 1-2 seconds, sometimes its lighting fast. I haven't figured out how to turn off its auto-balance on CPU but using PHM or XScale does the trick and things like the menu would still be slow. The GUI experience is poor in comparison to the Flame, and I don't find the Flame terribly fast.
Video: Related to speed probably, playing a 640x480 movie that the Flame plays at 150% the G900 can only play at 89% so you get dropped frames and a poor experience. The G900 does run at 150% when playing on on GAPI but has a problem. It looks like its only drawing the first 640x480 part of the screen and the rest is left black or the previous image, this might be a bug with TCPMP more then the G900 (maybe hardcoded for the 320x240 ratio), but since you can't use that mode you only have DD,Raw, or GDI and they are slower.
http://www.flickr.com/photos/8476722@N04/969516976/
Screen: And now we come to the meat of the problem. Though the G900 is 800x480 it packs that higher pixel count into a smaller screen. While a very nice screen, you seem to lose all that extra detail because the pixels are so close together you don't really see some of the detail unless you make it bigger (and therefore lose the advantage of the higher pixel count). Looking at an image on the Flame always looks much better then the same image on the G900. This picture will not do it justice but look at the calculator, that is the same bitmap on both but you can see that its clearer in the Flame, or the dashboard icon, etc...
http://www.flickr.com/photos/8476722@N04/969383384/
So ... ultimately I'm still not sure which I'm keeping. Now with a WM6 Rom possibly on the horizon for the flame, I definitely think I will wait and see if most of the Flame problems are solved, (though they can never fix the size :-P ) and re-look at them again.
If you have specific questions, fire away...