A 50% failure rate is _completely_ unacceptable; I might have a bad burn maybe one time in twenty or less, DVDs or CDs, on media that's bought on the basis of whatever was cheap at the time.
A consistent 50% failure rate on random media is unacceptable. An occasional 50% failure rate on random media does happen. Ralph probably is best off getting a new drive.
A failure rate of 1/20 reading back the same disc on the drive that you burnt is likely masking a large number of false positives. Try it several times, on several different drives, after storing it for a year, and some of your 1/20's will be 50%'s. And others will be fine.
Bryan