We know by now that we're going to have a new playable race - The Imperials, as long as you've bought the Imperial Edition. What does playing as an Imperial mean? Well among other things they aren't faction locked, which means they can be aligned with any race or alliance.
The Elder Scrolls Online is all about alliance/faction war - three alliances each containing three races. Depending on the race you've chosen, you'll automatically be put into the alliance they belong in. Now the Explorer's Pack, which you get with any edition of the game as long as you pre order, also gives you the same ability - any race in any alliance. So what's the difference? A lot of people it seems are getting confused and are asking the same question - Let's break it down a little and take a look.
In short, if you want to play a new race, buy the Imperial Edition, if you want to remove the faction lock, pre-order. If you want both, pre-order the Imperial Edition. You can bet your bottom dollar that both the Explorer's Pack and the Imperial Race will both be available as in game purchases. Although they may change the name of the Explorer's Pack and sell the items from it individually. It all depends on whether you're prepared to wait or even prepared to take the chance of whether it'll be available later or not. Hope that cleared things up for you. It certainly did for me.