Well, it doesn't burn it exactly right though. Many people using the 1620 to burn backups for their game consoles have found that it's -R burns wont boot reliably on their console.
This has been well documented on this forum as well as some PS2 forums - do a quick search (ScottFarcuz I belive initiated the thread here).
They don't always work on set top DVD players either -> a friend of mine has a Toshiba portable DVD player that plays -R burns from LiteOns and NECs without issue (but wont do +Rs unless bit set to DVD-ROM) but it wont play a -R from a 1620 for love nor money!
There's just something about it's -R burns that just aint quite right . . .