aren't medivacs too good? they are a medics + dropship combined and i suspect they can offer too much mobility to terrans - ball of healed marines and marauders can be problematic on its own when roaming around the map, but when you add a possibility of suddenly loading half screen worth of infantry into 6 medivacs to traverse a cliff or water and perform drop of doom on enemy base that was not directly within a reach? 50 infantry wipes whole base in 15 seconds and there is not much one can do to defend.
In sc1 healing/advanced units and transporting were 2 separate things and nobody could really afford 5 dropships at a time without sacrificing firepower of the army, yet i see medivacs in big numbers all the time in sc2 as a important part of triple M. I think that combining medics and transports into 1 unit was a bad move design-wise, because it streamlines infantry strategies too much. In sc1 terran had to be really committed to dropping to produce 6 dropships, now they are simply there to heal your bio ball. Ability to move whole infantry around sure is a nice bonus but now you simply have that ability without any deeper thought as a side effect.

Another example of such streamlined thing that complicates stuff would be current location of scan. In sc2 terran detection is always there because it is the same stuff that produces mules and everybody wants mules. If you happen to try dark templars you can be really sorry, especially when even 1hit kills trigger 'under attack' message and the scanner is impossible to destroy because it's on top of CC not next to it as it used to be in sc1. Does anyone bother to use DTs against terrans? There is no way in hell terran won't have a scan even if he is totally caught with his pants down by the rushed DTs.

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Q u o t e:
Another example of such streamlined thing that complicates stuff would be current location of scan. In sc2 terran detection is always there because it is the same stuff that produces mules and everybody wants mules.

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It is also true that if you always call down MULEs you won't have enough energy to scan for DTs.
And if you don't use your energy for MULEs in order to save it for scans, then you'll be at a disadvantage because you'll have less minerals.
You can just wait for the Terran player to call down a MULE and then attack, since you will know that he's probably out of energy :D