BioWare revealed during their E3 presentation that moral decisions you make in the first game will have an impact in Mass Effect 2, some more than others.
In fact it should feel like you never stopped playing hopes BioWare, with promises that the same will apply to Mass Effect 3. The fate of Wrex, of Rachni and of the Council got decided.
Some choices of morality were much smaller, like wasting a scientist behind some gruelling black-op experiments, or rescuing a government hostage from extremists. Deciding the fate of an entire species already thought extinct or indeed the very makeup of the Council is a little bigger.
It's not clear how many of Shephard's decisions will carry across but BioWare promises that players can "continue exactly" where their original Mass Effect story ends. Awesome.
Source: OXM