Ritek media is not known for its playback/readback quality -- it has rather poor reflectivity compared to other media. Ritek1 DVD-RW are actually not bad discs, but MKM (Verbatim), Sony and TDK are better. Sony the manufacturer, not the brand. Ditto on TDK.
ISOBuster only? You should be able to read it in
DVD Decrypter too.
That's a good NEC drive. However, the ability to read/write RW media is the first to go when a drive is dying. Next comes read/write -R/+R, and finally pressed discs. Not sure if that's the issue here, but it's possible. Not sure how long you've had the drive, if the home/office is smoke-free, how many burns, how often used for reading/playing, etc. Those factors all play into drive life.
DVD+RW don't need to be finalized. DVD-RW do.
Is using a DVD+RW an option?
Honestly, go to Walgreens and grab one of those TDK DVD+RW discs in a single-pack for about $2. It's been a few months since I bought some there, hopefully they still exist. Most drug stores carry singles.