A good dubbing is possible, but a good subtitling is easier to get right... I can read fast enough that flicking my eyes down to catch the written dialogue isn't an issue, and I normally end up mapping the words I've read onto the inflection I'm hearing... ends up feeling like they were speaking English the whole time. That might not work with languages that are drastically different from English (the more similar the words actually are, the more easily the illusion will happen) but it works well enough for me.
Bad dubs or bad subs are both terrible things though.