Speaking as a player with thousands and thousands of hours in CS... I definitely get why it doesn't appeal to some people. But what you describe about it is exactly why I and so many other people like it. The game changes very little, and pretty much only gives you guns and grenades as weapons, no fancy abilities or anything like most modern titles.

That unchanging-ness and limited toolset means that raw strategy and to a lesser degree reflexes are the only ways to get ahead. With the map designs set in stone, many with decades of refinement and balance adjustments, you get intimately familiar with every door, corner, and corridor. It becomes much more about predicting what the other team will do and strategizing against it, rather than just grappling with the game and mechanics.