*Points at Oblivion*
*Points at Demon's Souls*
*Points at Baldur's Gate*
Simply. An RPG with 3 view points. A First Person view like Oblivion's for each every character in your party. A 3rd person view like Demon's Souls, for each character. And an over-head view like Baldur's Gate's, if you want to control each character.
You control one of 3-6 Characters in your Party, depending on the difficulty of the playthrough. 6 Maximum for Casual. 5 Maximum for Normal. 4 Maximum for Hard. 3 Maximum for Insanity. 2 Maximum for an un-lockable yet to be named mode 
Huge game world with tons of places to visit. Not all big cities, and not all in need of aid. Quiet forests, huge Deserts, tranquil lakes, snowy tundras. World map like that in the original Baldur's Gate. But every area you can visit on the map is huge in comparison to the maps IN Baldur's Gate.
Typical classic WRPG fantasy setting. Orcs, Dragons, Goblins, Ogres, Demons... Etc.
You can rest at anytime you please, but you get more HP/MP back if you use a Tent. Tents are findable/buyable depending where you go. You are also less likely to be woken by enemies when using a Tent.
Thousands of different weapons and armors available for whatever classes you choose to be/ recruit for your group.
Thousands of spells for Clerics and Mages of all kinds.
Full character customization.
The game even features some RTS elements for when you get your castle/keep. You have to defend it twice from 2 huge armies. That's part of the story though so i wont go into that 
There is also a huge battle that you participate in around the middle of the game.
When you DO beat the game, you have the option to import your character. When you do this, you can continue playing the game after the final (story) bosses are defeated, being able to import your save file at any time. So if you find something new or gain a new level (You will) you can import it straight onto your next save game.
I probably missed some stuff but, yeah. That's pretty much the basics
