The NPV method is equally useful for comparing projects with different amounts of investment Is it right or wrong?

Not true. Since the amount of investment is different, in the case of the project are feasible, the investment of large projects will have a large net present value, and vice versa, the investment of small projects with a small net present value. Absolute return will appear to invest more projects, but the relative return (available NPV rate indicator), but not necessarily so.