The only way to know what a home is worth is by listing and selling it, everythhing short is an opinion. That said, the appraiser has the opinion with the most clout as he has to comply with industry standard guidelines - which get more restrictive as time goes by.
I have and have placed numerous $1M clients in NFulton, it's not an easy price point in some areas. Several of those Milton/Alpharetta/East Cherokee communities are slammed with distressed homes - combine that with the mortgage, underwriting, appraisal and general economic issues and it's easy to see why appraisals are an issue. If the closed comps aren't there to support value, then it's not getting past underwriters. I have two clients looking at unfinished homes just like this - and I'm having a very hard time endorsing their purchase.
I have an appraisal section that might be useful - several topics - http://www.hrmiller.com/atlanta-appraisals.asp
There are two likely explanations for your low value. First, the appraiser must use comparable properties that have sold in the last six months within a reasonable distance from your home. My suspicion is that there are limited numbers of homes in your price range that have sold in that timeframe and within a 5 mile radius of your property. Going back further in time is sometimes allowed but when values are declining, there is a "negative adjustment" to your value for the time since the comparable property sold. I would look at the comparables page of your appraisal to see what adjustments were made on the properties listed there.
A second, more subtle issue is that I have found banks to be extremely conservative when appraising more expensive properties because the limited supply of these home could create a much larger value decline if there are too many listed properties chasing too few buyers. Appraisers understand this and as a result are much more conservative with properties like yours. They work for the lender so there is a bias toward lower valuations on estate properties.
The bright side of your situation is you should consider appealing the assessed value of your property with the city and county to see if you can save on your property taxes and use your appraisal as proof of your property's value.
Best of luck
Timothy Brown | President
Academy Residential Mortgage, Inc.| email@example.com
11380 Southbridge Pkwy, Suite 200 | Alpharetta, GA 30022
678.468.5626 x110 | fax 678.935.1156 | cell 678.467.9959