This is so subjective, depending on the context within which you are evaluating a card, that it's hard to say a given card is or is not decent. There are many cards that could never see tournament play which find homes in EDH (Commander). But there are also top-notch competitive cards that are relatively terrible in EDH. Even in casual Magic, there's variance. If you're playing with Planeswalker Deck levels of power, then many more cards will be decent than playing against tuned casual decks.
A couple quick metrics you can use to guess how good a card is are the card's price and how often other people use it in decks, which are obviously related to each other. Make sure you consider the price relative to its rarity. Bulk commons that are less than 20 cents are usually not that great (though obviously you can still find a use for them in the right deck). In contrast, a 75 cent common might mean it's perceived by enough other people to be decent that the higher price reflects that (or it's just old and harder to find....). Uncommons will be a bit pricier than that. And rares are bulk if they're a $1 or less, but then again, bulk rares are still more interesting than bulk commons.
I'm not actually all that savvy on all the ways to look up what decks a card is used in, but I know you can search for decks on sites like MTGTop8 and MTGGoldfish. The former I linked directly to their deck search page, where on the left you can enter a card's name into the "Decks must contain following cards" criteria. On the latter, just search for a card, then scroll down to the "Recent Decks Using ____" section. A quick comparison of, say, Awakened Amalgam versus Stonecoil Serpent shows that MTGTop8 has NO decks with the former, but lots of decks with the latter, and MTGGoldfish similarly only lists 3 EDH decks that use Amalgam, whereas the Serpent features in a lot more decks and formats.
I want to emphasize that I don't personally know how good or useful those sources actually are -- hopefully someone else more knowledgeable can comment -- but I think they give you a quick idea of a card's overall usefulness.
But let's think about those two cards for a second. Is the Serpent truly more "decent" than the Amalgam? Well, the Serpent is a good creature all on its own, and can fit in a lot of decks. It has both defensive (reach, protection) and offensive (trample, protection) abilities, and its X cost allows it to scale well with the game state. In contrast, the Amalgam is begging for a deck to be built around it. You wouldn't want to put it into a deck that has a lot of basic lands, for instance. You also want to include a lot of land-fetching ramp like your Burnished Hart (or effects like Explore). Imagine casting a 4/4 on turn 3 (so a turn ahead of schedule) that becomes an 8/8 by turn 5 without putting any more mana into it. A 4-mana 8/8 on turn 5 is a decent threat in a casual game! I would want more than the typical 24 lands in the deck, and I would want a lot of utility lands that have "mana sinks" on them, to avoid having just lands and nothing to do with them. And THEN.... I would consider my Amalgam to be a decent card in the deck, since the whole deck is built to make it work well.
Analyzing another card, many people would consider a card like Demon's Horn to be bad, since it has absolutely no effect on the board state when you cast it, nor does it disrupt your opponent's tempo. And lifegain for lifegain's sake isn't valued by more advanced players. That said, if it's in a mono-black deck that uses its life as a resource to pay for effects or that cares about lifegain (effects like Sanguine Bond), then it's a "decent" card. The best card? Still probably not. But decent.
Sorry for the long post that doesn't actually directly answer your question. I know you wanted someone to point out objectively bad cards, but to be honest, I've only used about 3-4 of those cards, so it's hard for me to say. I can look at most of them and think of uses.... and I can also look at many and imagine better uses for that card slot. It just depends on budget and how much you'd be willing to spend to get a better card. Hope my long rambly answer gave you some food for thought! Cheers!
1 (100%)