Happy and warm may be overstating it. But it really is a half decent phone. Add in the fact Sony Ericsson provides free theme creating software ad you have a winner. This cell replaces a Motorola V551 which had an accident. It's leaps and bounds better then that phone in all but a few aspects. The Moto V551 has built-in bluetooth (which was never used by me) and a clearer screen (by virtue of its TFT technology). However, the V500A is more customizable, much better call and MP3 ring quality, and much much better reception.
A few other things I like are the slightly larger buttons and the more blocky feel, as it seems easier to handle and hold. However the Moto di have the rubber external shell that was a plus. I have not judged photo picture quality compartively. But, my guess is they'll be about the same. The V551 photo picture quality was horrible, and I'd assume the Z500A would be equally as bad (it is after all a phone first and foremost).
I mentioned themes earlier. I created a Spider-Man/MJ theme that I like quite a bit. You can download it it here. Better yet, browse to it from your compatible Sony Ericsson phone and have fun.