There are 2 projectile weapons in the game as far as I can tell, a rocket launcher very similar to the one in halo(no rocket jumping rip) and a plasma gun similar to the plasma/nail gun from quake but no jumping with it either.
Yes you can portal behind someone and shoot them through it while they can't see you but it isnt as much of a problem as it sounds like it would be plus you can use your grenades to shutdown enemy portals. Part of the reason for this is that you can only portal on certain surfaces and it's pretty easy to play around them. You can tell which portals are friendly vs enemy. Not being able to see through other players portals is still one if if not the worst things about the game right now though.
Played it for a bit and I love it. If you are looking for quake with portals this isn't it, it's very much portal halo like brimstone said.