The characters were pretty good, and the parts of the universe they did expand were well done for the most part. That said, changing the gameplay from largely connected and open worlds to corridors connected by loading screens robbed the series of some of its charm, as did the removal of uncharted worlds. Also, they played a lot faster and loose with physics and their lore than they did in ME1. There's nothing in the pseudoscience of mass effect fields that explains how Miranda/Samara etc. should be able to breathe in low-pressure environments with their chests exposed like that, even with breathing masks (could potentially make it worse actually). There's also the issue of how little sense it makes for combat. All in all, I think it was the weakest entry of the series plot-wise, but it was definitely the most developed character wise. This may have led to a lot of the disconnect between players of ME3's ending; people who entered at ME2 were more likely to see the series as being entirely about its characters, whereas ME1 fans were more interested in how the Reaper plot was going to turn out.