Unpalatable but inevitable!
The French system is not unlike the UK system, but most deductions are "ring-fenced", and don't just disappear into a treasury black hole.
As an average salary earner, you will find that the total tax burden on your annual pay is probably about the same as in the UK. You will pay a lot more in Social Security, but less in income tax. Social Security is deducted from your salary, but income tax is payable by you after submitting your tax return. Tax rates are banded; the lowest is 5%, the highest is 55%.
There are numerous deductions available when calculating income tax.
As a newcomer to France it would be advisable to get the help of an accountant to make your first tax returns.