In our last game we ran into a situation that I thought was easy to remedy. The party was hasted and the NPC caster cast slow on some of us so it was cancelled. One of the other players said it was not cancelled unless we failed the save on the slow spell. I have always assumed a spell such as haste/slow or darkness/daylight counters each other out no save. I know dispel magic can be readied and you have to make a caster level check to dispel it, am I wrong about this?