Climbing was the one of the most satisfying activities for me in the early TR's. There's a great sense of achievement while you're scaling a great height, and great realism and more time-value in the game even when you get it wrong. (I hate to fall too many times though. That does get discouraging!)
But the 'one route only' setup of Underworld is very disappointing, and cheap!
Tomb Raider isn't just about attaining goals. It's about exploring, or it used to be, but not any more.
You know what I'd like? A mountain-climbing game. Not necessarily Tomb Raider. But no-one seems to make one. A game where you can plan different routes up a mountain, and some will fail, and you have to strategise and ration your food, ropes and pitons, the way you had to learn to ration your save crystals in TR3. A game that's slow and laborious and tinged with possible failure at every turn, even after weeks of work and planning, just like climbing a real mountain. The early TR's gave me a taste for that.