that actually would be really cool. puzzles could be solved by launching grenades through windows, over walls, ect. to activate/kill, ect.
This isn't portal, puzzles are common in hl2 but I wouldn't expect many grenade launcher solved traps in my way in that game, It sounds so dull and random "Oh no, there's a massive brick wall in front of me with a small hole in it that leads to a flipping storage room full of c4, but how convenient, I've got this grenade launcher here, and I'll do the exact same thing I did the last 10 times -.-".
But yeah, I would Quite love it if they did something similar to the Resident evil 5 grenade launcher, It had many different types of ammo for that one gun, I believe there were explosive shots, corrosive shots, cryo shots, flashbangs etc. They could give the player an advanced type of grenade launcher in some place within the game, and let you switch between what kind of ammo you use, if you have it ofc.