Well I guess it depends on your definition of "impact"...
But either way you know the Genesis comic? All the decisions you took there will affect ME3 in some way. Then from ME2 we have the status of the Collector base, which squad members survived, some stuff from the DLC (Overlord, Shadow Broker and Arrival), Maelon's cure, rewrote/destroyed the Geth heretics and your romance situation. That's basically it.