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I passed 10th from ICSE (95.4%) and 12th from CBSE (74.8%). I will tell you one thing, The course is huge in ICSE 10th class. Literally HUGE.
In ICSE, you have to slog like anything, give exam on 11 separate papers. And read atleast two different textbooks in each subject. Specially in Maths, Physics and Chemistry. But it is worth the while. What you will learn in 10th class from ICSE board will help you throughout life.
Your point of view will expand. You will get exposure in variety of topics from Indian history to world history in detail. Learn to write English effectively, and have the ability to understand classic works like Julius Ceaser in its original form (yes in Victorian English). You will be compelled to learn to characterize persons from their dialogues. You got to remember the color changes in chemical reactions and the physics is awesome. And the best part is you will learn to code in C in 7th class and java in 10th(the fundamentals). Biology is detailed and you will learn every system in the human body. Also you will learn interesting concepts like osmosis. The bio paper has a few questions dedicated to practical utility of concepts studied. Some say Maths in ICSE is a bit easier. But do not listen to them. You will learn everything that comes in competitive exam