My first piece of advice is to be sure of the size you need. I have the Intuos A3, but I end up using only a section of the available surface. When I used the whole surface I found the increased travel was actually giving me RSI in the elbow. The size smaller would have been sufficient for my needs in the end. Perhaps you can rent one to try out?
I regularly use both - the larger Intuos at my studio and the lighter Bamboo for when I'm working offsite - and I'd say you can feel the difference in the build quality; the Intuos pen and tablet itself feel nice and solid, while the Bamboo feels a little bit light and flimsy, but not by much. While there is technically a difference in the pressure sensitivity of both models if I were to be honest I don't notice the difference much. However, if you're going to use it for painting you might well need that extra degree of sensitivity.
Finally be aware that if you've never used a tablet before it feels really weird at first, so don't be disheartened. It took me a week or so to get really comfortable with one and now I can't live without it!