Zaxxon was pretty rubbish in my mind, but I had only played the Spectrum version. Crazy Taxi on the other hand was one of the best Dreamcast games and has been wrecked in recent revisits due to poor licensing of the music or crap conversions.
Both are coming to iOS soon, and although the clip is really short it looks like this version will come with the Offspring tracks that made the original so fun. Zaxxon has been seriously upgrade to be nothing like the original, which I hope is buried in there somewhere. Still, if you like the inner-Death Star bits from the Star Wars games, this should appeal.