Hey, thanks for the feedback!
The smashing cubes were built on purpose. I think players getting smashed by doors, elevators or anything that moves is kinda hilarious in Sven Co-op. But that's down to personal taste I guess.
I thought about closing the portals as well but then I decides to leave them open, because sime weapons are only available at particular parts of the map (for example the sniper rifle, the double Uzi secret, the Deagle secret or the gluon gun secret). And if I close those portals, players wouldn't be able to get those any more if they wanted them.
For the snipers, they don't actually respawn, all the snipers you encounter are standing in the map from the beginning. The only spawning enemies are the soldiers in the cave you mentioned and the crocodiles at the beginning. I chose to let the soldiers respawn two times to re-populate a previously cleared area. Kinda to pat out the lenght of the map a bit but like you said, it's hard to balance, just like traps or puzzles.
If you found 6 secrets, I think you found all of them. There are 6 in total, it's also mentioned in the MOTD.
