I really don't like Sven Co-op. They change too many of the guns and remove some stuff if you play things like Opposing Force because Sven Co-op lacks the rope entity. Add on the fact that dying doesn't have any downsides in Sven Co-op and you don't really have to manage ammo and you get a lackluster experience of everyone running through the levels without caring about anything even on the hardest difficulties.
The maps MADE for the game might be good, but after trying out both Half-Life and Half-Life: Opposing Force with others, I don't feel like playing it.