RIght.. in theory this spell should be great. In play, it has always been a disappointment, to the point where I dont even use it. All they need to do is roll > 9. Having used it several times, ive probably put to sleep 2 montsers. Not worth a daily, imo.
At 1st level it is a somewhat so-so spell, but can still EASILY win you an encounter and is worth a daily slot for an orb wizard. Consider, if you can slow 2-3 of the 5 standard monsters that might be coming at you then you can focus fire for a round on one of the others and you've just deprived the enemy of actions.
Figure it this way, roughly: Each round you can just about kill a monster with focused fire at low level. So the monsters get approximately 15 standard actions in a combat, 5 on round 1, 4 on round 2, etc. Sleep will, when used in a good situation for it, knock 3 of those actions out right off, assuming you slow 3 targets. It will also on average cause the monsters to lose another 3 actions from sleeping. That's 6 of the monsters 15 actions down the tubes, the equivalent of outright killing 1 monster on round 1.
This is all BEFORE the huge optimizations of sleep you can get. The orb wizard can easily drop a -3 on one monster's save, and with a modicum of optimization can jack that up to around -7 by 8th level, though most of it now only applies to the first save. At 8th level the Orb of Inevitable Consequences can start to show up, which makes the spell auto-hit. At that point it starts to take on the dimensions of being the best spell in the game. With all the nerfs to save penalty granting effects its true heyday is over but even so a good solid orb wizard build in low paragon can pretty much win 1 encounter a day just with that power alone.
Making it work like the old AD&D version? Way broken. More way broken than the orb wizard was before it was nerfed way back, and that was pretty broken. 4e just is not designed along the lines of "I cast my spell, we won" like AD&D was. 4e wizards have a lot more chances to cast spells and each spell has less impact on its own. Wizards are still one of the best classes around but they aren't either insta-gibbing the encounter or else standing around tossing a dagger with nothing in between anymore.
You'll get used to it.