Matewis: I also thought Underworld was much weaker than Legend and Anniversary, but still kinda ok. How do you feel about TR:Chronicles? I never finished it but the first 2 or so levels left a really bad impression on me. Very 'meh'.
tinyE: I didn't like the episodic way Chronicles were put together, every level being a different time and event. It was obviously kind of rushed out and I always considered it a DLC/Expansion for #4.
Underworld was INCREDIBLY beautiful, but I couldn't help but feel that all the ruins started to look exactly the same. That killed it for me. That's why I always felt #2 was the best in the series. EVERY area looks and feels different, but of course, it's still the same story, unlike Chronicles. IMHO an absolute masterpiece.
Oh yes I love TR2, it's the first one I bought for myself, but god damn I got seriously stuck on several levels. The damned Opera House and that underwater ship in particular :P
TR3 is also great wrt level variety, though not nearly as much so as TR2. Unfortunately in TR3 I just hated some of the levels: the starting India levels were a drag and the Area 51 levels (the facility itself, not the cool desert levels leading up to it) were just plain horrible.