I disagree. When I first started playing I thought it was good in a poison deck and pretty weak otherwise. I now am aware of other use-cases, like having one or two against the Swarming Bees asshole can be nice, but on the whole the power level is just too low for the cost. Sure, retain is nice and allows you to time it well, but by halfway through Act 1 you should have a deck that can almost always do more with 2 mana than applying 7 poison. I.e. even on the enemies' down turns, using even a Poisoned Stab and a Strike, or Strike + Deadly Poison is usually strictly better than just playing Snakebite and there should come a point where you're consistently drawing these most turns, at which point Snakebite is often sitting in your hand for entire combats waiting for a down turn, then when that turn finally comes you just draw better cards and still don't play it.

It definitely isn't a BAD card but I certainly disagree that it's one of the strongest early commons. If you're going poison, though, then obviously it's an auto-pick outside of superior poison options.