What makes a handlebar good or bad? Weight? What else?

They come in different widths, radius and curve shape. Many small riders use a bar that is too big or too deep. Get one that suits your size and style.
You can have a bar that is too light. Ultra-light have little safety factor, esp for powerful riders.
Grooves can help conceal cable runs for better comfort. Campy systems need 2 grooves, for brake and gears.

how do you find the right curve shape and radius? Is it just trial and error?

Griptacularness. Seriously, though, the specifics are different for everyone. I've tried a few different bars, and currently really dig Nashbar cowhorns. If you have friends that ride, see how you like their bars. Try the same with different bikes at your LBS.

Grab a Ritchey BioMax ..

I can second the biomax...I definitely like mine. I too would look at trying out the Nashbar one though...saw that in the catalog the other day.

Specialized has some body geometry ones that are pretty ergo to...

Actually, Campy systems don't need any grooves. They're designed to be routable in parallel across the front if you wish.

Bar shape and width can have a great deal of influence on comfort. Wider bars allow you to ride with your arms further apart allowing your chest better expansion for improved breathing. The cost, of course, is in weight, but it's all about priorities and trade-offs. Broad shouldered riders might consider wider bars.

A handlebar that's labeled "ergo" may not be very ergonomic for any particular rider. It depends upon the intended use and the tradeoffs one is willing to make.

What makes a good handlebar? Why one that doesn't break

I've been searching for the "perfect bars" for a while now. I'd like something with medium drop and reach, fairly stiff, and flat on the top. My preference is to slide my hands along with top without having to angle my wrists down when grabing the hoods.

I noticed while watching OLN that quite a few Tour riders (like Lance) have their brake/shift levers shoved way up the bars. By doing this, the top becomes flat such as like I'm looking for. So far the best bars I've found are Ritchey anatomic's. I set the STI levers slightly above the bottom drops and then angle the bars slightly upward. This is the best compromise I've found so far.

Not sure this info helps at all but there you have it.

Ed

i've got 4 in my garage now - 40, 42,and 2 44s.

I hate the ritchey wcs bars. the 'ergo' section digs into my palms .

the bontrager race bars i've got are ok, but the flat section on the end of the drops isn't long enough. I like a flat section there long enough to rest my hands, like the old fashioned round drop bars

the prima 199s?

no extension on the bottom at all, I guess to save weight.

any way I got em all on ebay , just to try em out.

I think now I'll just get some traditional drop bars and go back to what I rode on 15 years ago....

i like the traditional drops that came with my motobecane. They just plain feel good.