Firstly, this will take you many hours to get the most from it. So if you liked "Knights of the Old Republic" and "Jade Empire", you'll have some idea what to expect.
This is the next step up, and its quite some step.
After an initial mission on Eden Prime, you arrive at a huge space Citadel and the RPG elements familiar to those in the aforementioned games kick in. All the dialogue is voiced superbly, and branching stories and missions depending on your stats kick in.
For gamers into astronomy this is literally heaven. You can travel to many Star systems and land on numerous planets, survey elements and recover mysterious artifacts as well as completing sub-missions. The planets are beautifully imagined, with glorious vistas containing Binary suns, Planets etc. The attention to detail is breathtaking.
Unlike TES Oblivion, you never lose sight of your main objectives, and I personally found this game beautifully paced and the story engrossing.
Like KOTOR, you gain an empathy with your main character and squad members with whom you interact.
A lot of people have mentioned glitches with this game and there is a small amount of slowdown due to the RPG probability calculations, and certain sections of your MAKO exploration vehicle when the camera goes a bit haywire, but these are miniscule and not really a problem.
The menu or Mission computer is very well designed and easy to use.
If you liked the previous mentioned games on the XBOX or are really into the concept of future space exploration, this game is a must buy. If you want to get lost in a more adult RPG, again I would recommend this without hesitation.