The construction of the Brooks Brother has really fallen or at best flat lined these past years. First and foremost, they no longer use Martin Greenfield for its Golden Fleece suits for both the off-the-rack and made-to-measure suits, so the handwork has fallen. They have switched exclusively to Southwick for all suits.
As for the 1818 line, they were never really that special. They had some fusing in the chest and lapel construction. But they were really good workhorse suits. I have a closet of them in both the made-to-measure and off-the-rack programs, and I love wearing them. And the current Golden Fleece construction isn't that much better in my opinion. It is a full canvas, but it doesn't seem that much better.
The one redeeming quality about the Brooks Brothers' made-to-measure program was the vast array of options one could choose from. This was in addition to style features like lapel and pocket options to the nature of the fit. If you have a very experienced sales associate and/or tailor, you could describe the fit you wanted and actually get it. This was also due to the nature of the fact Brooks Brothers had four pattern styles to pick from. Lapel width and style could be modulated based upon the stock fit chosen. For example, when I wanted a larger lapel I chose the Madison Fit and had many adjustments to get the fit of a Fitzgerald fit.
Then of course, you could fix a lot of fit issues too. Low shoulders, darts under the lapels, sleeve rotations, button stances, higher armholes (my favorite), double darts on the trousers, and waist suppression are just the few things the program could take into account to.
After having a suit made for me by Ralph Lauren and Brooks Brothers, the construction and quality of a Ralph Lauren is far superior to a Brooks Brothers suit (at enormous price differential), but the list of options on a Brooks Brothers far exceed the Ralph Lauren program. And based upon the Samuelsohn suit I bought from Saks' In-house collection, the construction there is far better than a 1818 or equal the Golden Fleece construction too. I haven't tried the new Hickey Freeman stuff yet, so I can't comment.
At Brooks, My recommendation is to first start with the lapel style and width model that you want. This is based upon on the fit you start off with, i.e. Madison, Regent, Fitzgerald (doesn't come with peak lapels), or Milano fit. Then pick the size in jacket that fits your shoulders THE best. Don't mess with the point to point. Everything else can be customized. Also, make sure that the suit being used for the measurements is made in America because the American and Italian patterns differ, and from a very recent or current season. Also remember that you can mix and match trouser fit. Like my example above, I had them make me a new Madison cut jacket but chose my standard Fitzgerald trouser pattern. Let the tailor and sales person know exactly what you're looking for in a suit. Be as exacting as possible.