This is much better than Lab Man in Doomsday:
- It costs 1 less mana.
- You can draw up to 3 (!!) fewer cards with it to win the game
- If you have zero cards in your library when its ability resolves, you still win. So unless your opponent counters Doomsday or the creature, you just win now if you can get your library to zero cards. (Before, you'd have to get your library down to zero cards, THEN cast a draw spell, THEN hope they don't have removal OR bank a counterspell for it.)
These are all gigantic improvements. Often in tight games playing Doomsday you will find yourself one mana or 1-2 card draws short of being able to combo off and will have to pass the turn, usually resulting in a loss. This happens a lot -- in maybe 25% of the games you play where both you and your opponent have reasonable draws, I'd say. It's especially common against shops, where the presence of a sphere will tax you one or two critical turns because you either couldn't afford Lab Man, or couldn't afford to cast a draw spell after he resolved.
Also, crucially, because you don't have to include as many card draw spells in your piles, you can now include more counterspells, duresses, artifact removal, or cards like Time Walk and Yawgmoth's Will in your piles to provide extra resilience.
Basically, this card takes the bare requirements for Doomsday to be a win down by a huge amount, and therefore either speeds up your kill, improves its resilience, or reduces the number of resources you'll need to win off of it, all for basically free over Lab Man. These are huge improvements that should be tested for.