When you say that NES Xenophobe is one of the worst, on what do you base that claim? Less aliens per screen? Smoother screen transitioning?
It kind of grows on you the more you play it. The trick is to think ahead about how your shots will wrap back around the islands, and how you can get your opponent by surprise.
Yes! That mode is great fun and a really welcome addition to the game!
I have heard that the Tengen version of Tetris on NES has 2-player co-op play as well.