In LR2, I believe LNs work similarly to stepmania (someone please correct me if I'm wrong). I think they require you to press in the beginning, but do not require lifting right at the end of the LN. I have no idea how releasing early works, or if repressing does anything in LR2, so someone who actually knows about LR2 will have to cover that.In LR2, you are judged for timing the press as well as the release. You are judged once, I suppose based on a combination of your press/release timing. If you press too late or release too early, the LN is missed. Missed LNs cannot be repressed.
On the other hand, LNs in O2Jam are much harder than LR2 or o!mI don't know too much about O2Jam, but I'm pretty sure LNs are equally hard in both games when ignoring timing windows. I'm also pretty sure LR2's timing windows for LNs are slightly harder, maybe depending on the song's timing difficulty.