As a Lions season ticket holder for many years, I can say that the only things that the old BC Place and the new version have in common are location and the base concrete structure.
From the exterior, the entrances have been completely re-done, with much more glass and steel; the exterior facades are dramatically improved with the clerestory lights; the masts, the roof, and roof lighting have become a new icon for the City. I can't emphasize enough the improvement to the gameday experience of having a retractable roof. On gorgeous summer evenings, seeing the blue sky change to the evening is great! And, of course, the closed roof comes in handy on those rare rainy days.
Inside, the seats are wider (finally, with cup-holders!); the HD screens are amazing; the ribbon board and scoreboards are a dramatic improvement; the redesign of the concourses (with video monitors EVERYWHERE) is a serious upgrade; the washrooms are better; and ingress/egress are easier without the airlocks/revolving doors (though I do miss being "launched" out the doors at the end of each game).
Essentially, we got a new stadium, in the same location. BTW, the location has always been one of the best points about the stadium. Very walkable, transit stations nearby, lots of excess office parking, and many, many options for restaurants and bars in the vicinity. Also, the bonus of a very nice tribute to Terry Fox, immediately outside the stadium, also dramatically improved over that original design nightmare.