The downside is actually pretty big. Zombie Chow was good because there was no downside early in the game. This one creates a minion, that eventually you will need to take down, plus the opponent can make a use of it with numerous buff spells and minions.
This looks like a strictly aggro card to me. If you can build a board quickly (which with a 1 mana 2/3, you can), you can easily kill the 0/3 taunt and it shouldn't set you back too much. The only really bad thing is if this guy is on a wide board and your opponent clears the whole board and get a free taunt.
I don't see it. This card might as well read, "Can't attack for 2 turns" because that's what summon a taunt it can't kill on it's own in 1 swing means. Also Even Shaman plays buffs so there is an aggro deck that can abuse this. Your opponent will just go face regardless knowing their minions are protected thanks to this taunt you graciously gave them while they laugh at you as you poke at this stupid little taunt or waste a resource on it.
The whole point of having a statline like that for 1 mana is so it can trade into some small minions at the same cost, in theory good against aggro but if you can't reach said minions then it is pointless.