Well, if you take LGA as an example... there are times of the day when you can push off the gate and go straight to the runway and be first in line... there are other times during the day when you can push off the gate and be number 50+ in line.
With a slot system, they are going to have X number of departures per hour, and each airline can bid on the time of their choice. The overall goal being to shift the flights to be more evenly spread out throughout the day.
The big problem with LGA is the lack of gates. Frequently planes push off the gate, knowing they are going into a 2 hour plus taxi, because planes that have landed need the gates.
The idea of fixed slots sounds great, but isn't realy going to address the issue that there are certain times of the day that people want to fly, or need to fly to make their connection. Moving a 3PM departure to 12N sounds good on paper, but all it really will do is make passengers go to whatever airline DID get the 3PMish slot to go where they need to go. If there are not alot of flights at 12noon, it is because there is not alot of demand for it. No demand = empty airplane.

The slots would in theory ease congestion because you won't have 10 airlines all pushing off the gate for a 3PM departure... One will get 3pm, another 3:02, another 3:04, another 3:06 and so on... in theory it should work well..... for ATC. In a practical, real life situation... the planes will still be pushing off the gates to make room for inbound flights during peak times due to lack of gate space..... but what happens on the ramp isn't an ATC issue since the ramps are controlled be the airlines.

so, does anything get better.... not by much, except for the ATC folks, and the FAA and Port Authority will get to collect higher fees for prime time slots....

spray a pile of crap with perfume, and it's still a pile of crap.