Read in the hardware NEC forum to find out about bitsetting for your drive. You need to flash your firmware to do bitsetting, it's not hard to do, just read a little. I also have the 3500, bitsetting works, sets your burned discs as DVD-ROM. Store bought DVD's are DVD-ROM, so it makes your burns more compatible as Zevia said. Players recognize them as a regular DVD.
If you don't bitset, then - discs are more compatible, especially with some older DVD players. But bitset, the + become the more compatible.
But a majority of new DVD players I think are compatible with - , + , and DVD-ROM, among other formats. Hope that helps you.
Personally, I'll only be going with + discs with bitsetting. I've only burned a few - discs, and may not ever burn anymore.