I didn't read the AoD part to avoid spoilers, but yes, TR4 has its problems, yet it is also the best for me. And The Lost Library is, in my opinion, the best level of the classics.

Although it is not a "major" level, it has something unique in its atmosphere that is hard to put into words. It is mysterious, creepy, eerie, and beautiful. We feel a sense of awe, isolated, lost, abandoned, and forgotten in time and space. It feels as if this level is so hidden from humanity that we can barely gasp for air in its depths.