All those cards you listed are rates, though. This is a common. I'm talking mainly about arena here
I actually think its okay. Not great, but you can do way worse
You could do worse, but most likely don't have to. There's at least 10 common 3-drops I'd rather have (see my list about a page ago).
This card is not bad on turn 3 on an empty board if your opponent doesn't have a 4/3, Soulfire, Shadow bolt, Eviscerate, or coin+Truesilver. You'll probably get at least 4 face damage, and force him to not play a big 4-drop. But the problem is that there are too many ways for it to just get blown out, especially later than turn 3.
What about the other cards? Nerrubian Egg (2 mana 0/2, deathrattle: summon 4/4) could be good if we get a sacrifice outlet of sorts (something that kills your own things for benefit, Warlock has a few), Undertaker is a Johnny card that just seems fun, though not nowhere near comparable with Mana Wurm, at least not now.
Egg and Undertaker seem like they'd be good in the right constructed decks but might have a hard time cutting it in arena. Shade is the best of the neutrals revealed thus far, and it's basically like Panther.
The class cards, however, all look pretty good. The Druid one gives actual hard removal with a smaller drawback than Naturalize. The Warrior one is yet another weapon, which is always good. The Paladin one seems like good stats -- at worst it turns a token into a 4/3 which is worth the 3 mana spent on token + secret. And the Rogue one is a big 4-drop.
It looks like that Deathrattle is meant to be a drawback, no? I mean, that's compared to a 4/5 with nothing special.
It is a drawback because usually your opponent will kill the minion, which gives them better control of what bounces, unlike with pandas. You can't follow this up with a big 5-drop, because it's likely to bounce back. But if you follow up with like 2-drop + 3-drop (preferably with battlecries) or a weapon or something, there's not that much of a drawback.