I have to disagree with the Soul Calibur comment, the original SC is the clear front runner in that series, the additions only seem to serve to weaken it slightly, and im not sure why.
3rd Strike is definately a better sequel to the past SF3's, and with most fighting series, some sequaels are better, and some worse.
Quite often, if the sequel actually makes an effort to build on the original, it is on some level better. But the most common type of sequel, which is put the same game into some poorer level design, doesnt usually work.