I see it is on sale and would like to buy it, but I don't want to get into the same situation as the original mount and blade - I don't want to spend all that time on it just to find out there is no final goal, no end game.

Which of the games? There are quite a few in the M&B series. The new Bannerlord?

Also, the original game most certainly has an end as I have reached it several times. The end goal is to unite the whole of Calradia under one flag. That is done by your faction conquering every single town and castle and then hunt down every single remaining troop and beating them.