op implies that after half life 1 engine cs 1.6 it wasn't same game anymore, which is a common sentiment among people who were there. first, besides I think "urban terror" which was a mod for q2 engine, cs was the first "realistic" shooter, so if you played it beta to 1.6 you were part of the creation of the new genre. second, most of the mechanism from half-life engine were still exposed and the path from beta to 1.6 was at least in part about tweaking your cfg to give you a little edge. each new release would nerf and remove some "exploit", and it was kind of exciting in its own way. third, cs after it got bought by valve and later cs:source became big publisher game, explicitly "e-sport", crystallized in the conventions, big and flashy, one of many "realistic" shooters, that came to dominate the shooter genre.