I've played BG1 and gone all the way through around 3 times I think. Each time I go a little further and venture a bit more into areas I steered clear of before. I am currently gearing up to play through the entire trilogy from BG1 to BG2:ToB.
As for reloading I have only once gone all the way through without reloading. I played on normal difficulty which is more than likely the reason why, but it still isn't easy regardless of what level you play.
As for differences, much of what I would say has already been discussed. BGII gives a lot more of the 'hand to hand action' fighting, than BGI, and the character interaction gives more life to the game.
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