Well, a side by side comparison may be in order.
I am a massive fanboy of the series, but in my opinion, the first game's cover is not very good at all. Decent, but way too cluttered. The second game's cover is absolutely terrible and generic, but who cares, we finally got to play Commander Shepard again! But the third game's cover actually looks alright (once again not great, but better than the others). It has much of the same effect as the first cover without the awkwardness and crowding.
But, all in all, I'm not totally certain why we're having this discussion. The fans would buy it even if the cover just had a jellyfish on it[1], so in the end it doesn't really matter.
[1] Just to be clear, not the image of a jellyfish, a life one.
That stings.