Here are the different effects you can get out of Bard:
1. +$2, you may discard a Treasure to gain a card costing up to $4.
You get to choose between an Ironworks-ish effect and a terminal Silver. That's super versatile and fairly strong.
2. +$3, +1 action
That's super good at hitting $5.
3. +$2, you may trash a card from your hand
That's Salvager. Salvager is a very powerful card.
4. +$3, +1 buy
That's strictly better than Horse Traders without the reaction part, which is already a decent card.
5. +$2, you may topdeck a card from your discard pile
That's strictly worse than Scavenger. Probably the worst Boon you can get, it sort of sucks if you get it without anything good in your discard pile, but even then it's no worse than having a Swindler hit an Estate or having a Militia hit two.
6. +$2, gain a Silver
That's Explorer. Considering that you only paid $4 for the card, that's very good tempo in the early game. You probably don't want it in the late game though.
7. +$2, +1 card at the end of your turn
That's great at hitting $5 and in general.
8. +$2, +1 card
That's a bit more awkward than the above, but still pretty good.
9. +$2, you may discard 3 cards to gain a Gold
If you actually want the Gold, that's super strong. If you don't, well, it's not.
10. +$2, Cartographer effect
That's a lot better than Navigator, which doesn't say much necessarily, but the difference is really big.
11. +$2, gain a Wisp
Gaining a Wisp in addition to the terminal Silver is pretty good for most decks.
12. +$2, Dungeon effect
Again, that's super good at hitting $5.
Half of these make it super likely that you hit $5 on turn 3 and/or turn 4, either allowing you to open Bard/Silver and have realistic hopes of hitting $5 twice, or Bard/trashing while still having a decent chance of hitting $5 at all. The other ones are still on-par with most other cards for hitting $5, and they give you stuff like trashing, free Wisps, and sometimes something of very low utility in addition. All in all, it doesn't do anything amazing, but it is more than sufficiently strong at what it does, which is early game economy.