Restaurant Alimentum has to be the best dining experience in Cambridge. I don't usually go for 'ethically sourced food' but rather what tastes best - but this place does both! A great meal and wine selection, awesome staff, and lovely ambience. I heard that people are travelling out of London in order to eat there, and I don't blame them - a faultless restaurant.
Browns (for me) is dated and has let itself go a little bit, Loch Fyne however remains a great choice for seafood.
If you're looking for a good old pub - I agree with the post above - The Eagle is the place to go!