Think of prior Elder Scrolls games and add an online portion to them - this is basically what TESO will be like.
@OP: Don't believe a word of it. If you have played previous TES titles and enjoyed the gameplay, prepare yourself for the fact that this game will play very differently and you will not comfortably transition. There will be a learning curve: it will not play like previous TES games due to the design choices made by ZOS.
Best thing to do is get your hands on any of the myriad MMOs out there (most are free to try) and play with it a bit to get a feel for things. World of Warcraft is a good start, but a more accurate depiction would likely be Guild Wars 2 (which comes out on the 28th) as to what ESO will play like.
Other than that, it might look quite a bit different than other TES games as well, with a more stylized, simple look, especially if you are used to Skyrim.
It will be more or less the same lore and all the races are there except Imperials, but don't expect this to be like playing TES with friends. They have said numerous times it is most certainly not that.