Greg Howson of The Guardian (UK) says the exploration aspect of Mass Effect feels a little undercooked, the enemy AI is erratic and there are framerate issues, but he thinks the flawed epic deserves a wide audience. He recommends Mass Effect over Mario & Sonic at the Olympics and Kane & Lynch: Dead Men, which also come out in the UK on the same day. He also briefly covers the other two titles.
(Howson is the video game reviewer for The Guardian. He has not published his Mass Effect review yet.)