It's an RPG with a huge amount of different directions to go in. I'm not going to go into the main quest plot but you choose which race/species you want to be, customise your look (there are about 40+ setting to tweak face shape and so on) and you can then go about your merry way. The game is HUGE with quests all over the place.
You can ride horses or go by foot, stick to the paths or go into the miles of countryside, ruins and dungeons, spend your time bartering with shopkeepers or fighting in the arenas, learning more magic or... etc. It's endless! Also you can join the various guilds to do jobs for them, I'm in the thieves guild myself though I'll probably end up in all of them eventually.
The game is hugely pretty, you can see screenshots here:
http://www.elderscrolls.com/art/obliv_pc_screens_01.htm
And it is very
very addictive, so be warned!