Is there any difference between 想, 觉得 and 以为? 想, 觉得，以为 all mean to think. But is there any subtle difference between the three or tense difference? When would you be more likely to use them in context?
以为 is mostly used for: 


wrongly thought/believed 


like: 我以为你死了！ I thought you were dead!

觉得 is closer to:


feel/think (of an opinion)


like: 你这样说，我觉得非常不靠谱 What you said is totally unreasonable.

想 is close to the English:


think


like: 我想这个案子肯定有猫腻。 There's something fishy about this case.

In Chinese the idea of English 'think' is hardly ever used - even in English it's mostly just a buffer or fluff; if anything 觉得 is the closest.