Navigator is nice when you want to quickly cycle through to a key card, and don't have much draw. I recently found it to be quite useful in a Rebuild deck. The terminal silver helps you reach $5, and the navigation helps me skip past hands that either have no Rebuild or in which Rebuild and my lone Duchy collide.
I think this is very true in the rare cases where your key card is not a terminal Action (Rebuild being a great example). In my experience, if I'm trying to cycle to my Witch or Mountebank more often, Chancellor and Navigator tend to do more harm than good.
I recently had a single Tactician deck where Navigator came in very handy on my Tactician turns. Many Tactician hands start with an empty discard pile, so it was nice to skip past five cards, getting me to my next shuffle—and my next Tactician hand—much faster.
Navigator reminds me of Chancellor, and yet I feel that it is still fundamentally different from Chancellor. The situation above is an example where Navigator is definitely better than the alternative.
Thing is, if you play Chancellor when you've reached the end of your draw pile, it's basically a terminal silver. If you play Navigator in the same situation, it's a terminal silver that also triggers a reshuffle. Whether that's a good thing or not depends on the quality of cards in the clean-up that turn, but it does mean that you tend to see the Navigator itself less often.
The way I see it, you have less control of your deck reshuffles with Navigator, especially when you choose the discarding option. The rearrangement option of Navigator is nice, but it's hard to make use of it since the card is terminal, unlike Cartography and Apothecary. At best, Navigator is a good support card when you have actions to spare and draw capabilities. Otherwise, it really tends to get in the way of the power terminals.
Personally, I feel it's discard option is better, but using the discard option of the oracle and catacombs somehow feels more rewarding. The tag-line "Navigator: As bad as it looks" was meant to be more of a stab at it's card art than the effect itself.
