I don't think this is an exhaustive list, but I'm pretty sure playing a vanilla ME: 2 results in:

- Garrus was recruited
- Wrex was recruited
- The feros colony was not saved
- Shiala, the asari, was killed by the Thorian
- The Rachni Queen died
- Shepard killed Wrex on Virmire
- Shepard had no romance
- The Destiny Ascension, along with the council, was destroyed.
- Udina was named counsellor
- Ashley survived Virmire if Shepard is male, Kaiden survived Virmire if Shepard is female
- All side missions and DLC content are considered as if you did not complete them

Honestly, it is pretty crappy choices they pick for you.