I remember it having a nice subtle balance - you couldn't afford to just let terror missions go unmolested because you would quickly lose funding. On the other hand, you couldn't just grind soldiers out because you needed them to progress with skills, etc. for the endgame... although there was a sort of plateu around when you got armor and psi-ops where things got boring between, say the 70% and 95% where you were just waiting to capture that one thing you missed in the earlier missions... from what I remember, that was the worst thing; There were like 2 or 3 things you needed for your tech tree that only appeared in early missions and they were really difficult to get after that.