I thought Mass Effect was really weak. Insanely repetitive "land on planet, drive around, find little things" killed the experience for me. Less planets and a more dense environment imho would have made the feeling a lot better, because there was quite a bit of good content, it was just too scattered. Imagine Fallout 3 on a map 10 times the size, but with the same content.
I found Jade Empire to be a lot of fun, but probably because I didn't expect much from it. As soon as I figured out it was an action adventure, I just played it that way.