It may be more useful to look at when it's good.
It's good against junking, whether by the opponent or self-junking-for-benefit cards (watch out for the dreaded "if you do" wording, though...) and against handsize reduction attacks.
But it's draw effect as the only positive has to be used carefully. It only works with disappearing money engines. In BM, it's no better than Moat, and Moat/BM isn't a thing. Even in an engine, it's not enough that you just have "non-drawing Villages." Villa/Watchtower or Shanty Town/Watchtower may be terrible unless you can drop most of the cards that you've drawn on the table before you play your next Watchtower. Villa/Watchtower for 3 cards/Villa/Watchtower for 2 cards/Villa/Watchtower for 1 card? Not good. You've just played 6 cards for $3 and +1 card. You need non-terminal cards that reduce handsize for benefit; even cheap ones work (Pawn for +action/+coin, Oasis, Poacher, Warehouse)
I've skipped it on plenty of kingdoms where there was no junking, or if the game was a clear BM or deck-drawing engine. You feel pretty silly drawing a Watchtower into a 10-card hand.