I know what you mean about it being a brick. That was my thought too when I first saw it, but in the end it's not that bad. My previous phone was a Nokia 8810, so the change was even more dramatic for me.
But when I measure it up, the 7650 is about as tall as the 8810, it's only about 1cm more wide and 0.5cm more deep.
It's certainly smaller than the phone you suggested, only maybe a tad more wide.

Yes, I know you'll have to change your carkit to if you want a 7650. You'll have to change your carkit if you want any model other than a 6xxx (or some 5xxx) models. It might be worth it though.

The camera functions is a nice option, but the novelty of it wears off quite fast. I don't know anybody who also owns a MMS capable phone, so I can't send the pics to anybody. (though that will probably change in the immediate future) The quality of the pics is not good enough to use the phone as an actual digital camera. They are only 640x480 and it's only usable in well-lit areas because it lacks a flash.
It does have it's purpose though, and I like the idea. Something can be said for always being able to take pictures of people in embarrasing situations!