Giana sisters bundle, yay or nay?
Yay. As I said above, it's a strong platformer in the PS1/Saturn style era of mechanics which makes it quite fun to play. It's gimmick is the ability to switch between a "hot" and "cold" worlds and likewise between the two sisters which alters the world a bit, this is where most of the challenge comes from in the game.
There is a demo, so go ahead and download that and try it out for yourself. I won't lie and say the game is too much more than that, but it's still good fun and will offer enough variety in how the stages are laid out in what you don't see to keep going, plus any sense of completion desire platformers can cause.
I would have enjoyed it back in the day for £30 on my PS1, right there with Kolona and Rayman, for the reduced price now, it's an easy purchase. Not the greatest of it's type and I wouldn't recommend it over Rayman Origins and the like, but it's good and worth the time I spent on it.