I too have a Defy3 2009. Have posted about it ad nauseum in the past. Can say that for me it compares extremely favorably to my 2008 Cervelo DA and the aluminum frame actually absorbs shock better than the Cervelo which is as expected, a super stiff racing ride.
The frame on the Defy3 is excellent. I've had zero problems with fit and comfort on it, and it's my primary long-distance training bike. (I ride 60+ miles pretty much every weekend, and have a 20 week unbroken stretch thus far including today.) If you're going to compare it to another bike that you spent a lot of time on, of course you'll find fit differences to criticize, but I think that's a function of the Defy than the reality of the small differences in bike fit. You an absolutely set up the Defy3 so it's pretty aggressive - I'm lower than most of the roadies in the drops who ride the $5k bikes.
It uses pretty basic minimum type parts, but they work so well that I really have had almost nothing to complain about. The only thing that I do notice is not the fault of the bike, but is the Sora-2200 groupset that the bike came with, and which I still ride the original cassette (I only ride this bike on weekends since I'm on a trainer the weekedays) which is obvously inferior to DA, but still works so well (near flawlessly actually) that I can't justify replacing it.
I bought my Defy3 new from the LBS for $650 on a holiday sale. (Normally priced at $750.) My bike has small amounts of wear and tear but is still a great ride; I'd say it's worth at least $350, or roughly half off its new price on the open market. (Which means that for $350, you get a bike that's pretty much as fast as a $10k road bike, which is a pretty dang good deal if you can score it.) I suspect that if someone else was selling my bike at the insane Craigslist prices I see nowadays, I wouldn't be surprised to see someone try to unload one at $500+ (I wouldn't buy it at that price.)