EDPs are more concentrated and are also often different formulations. Usually they are very recognisable as being the same scent but with different emphasis. They usually last longer than EDTs - that is the point of them really, it seems they often have a less diffusive opening, they may have less of an impact at first. So they usually have great longevity and slower development but may have less sillage (scent left in the air), especially at the beginning. .
This varies from perfume to perfume though. Opium Pour Homme EDP is not short on sillage.