The concept feels like it has something there, but it never really... expands upon it.  From the bit I did.  It's lacking a lot of feedback, and it's very slow paced.  Especially considering you have a grenade launcher.  Movement was very floaty and once again without any feedback.  Some finer points:

• Like I said the idea seems interesting but the game itself seems completely counterintuitive to it.  You're given a grenade launcher, and then told to only fight one enemy at a time.  Which takes away the main fun of a grenade launcher.  I feel like changing up the weapon if you're being made to fight a single enemy at a time would help.  A pistol or something similar.
• Although my recommendation would be to tweak the main mechanic and rather than making them invincible when they're together just increase their health and damage.  Maybe have them combine into different types of enemies etc.  That way it could vary up the gameplay while still fitting the theme and the main mechanic.  Then when you use the balloon gun, it could "separate" them which would weaken them and make them easier to kill.  
• As I said as well movement felt very floaty which didn't help too much.  I feel like increasing gravity or something to that effect would help there, though not sure. 
• The game felt very slow paced overall, though that's down to a ton of factors so I can't really pinpoint one main one to comment on here.

That's about it I think.

Like the idea and gameplay is good, the balloon gun is a brilliant idea. The only improvement is to maybe too make the game have a story and more levels.

Neat game idea. Of course it could use some fleshing out, but for a first game this is not bad at all. Good job!

This game has a cool main mechanic. I think if you keep working on it, you should add some animations and music. 

A really cool mechanic idea for a game

Good game. You can polish graphics a bit. Consider playing my game

Its very intresting game. It need some more time but its great start. Some music and more information about what to do will be great. 

If you want you can check our game. Thanks!

Fun game! It needs a little bit of work in the graphics department (like lighting), but the core mechanics and gameplay were enjoyable! :D

unfortunately the enemies were a little buggy, and decided to float in the middle of the room. But good job nevertheless! 

If you have time, can you rate our game too? 

Hey there @petifox. Your game is just fine. It is a bit boring in my opinion. But anyway. Good job^^

I would be happy if you playtest our game too :D Here is the link: https://itch.io/jam/brackeys-5/rate/925955

you are to shoot the enemies with balloon gun 

then, you are to bring them down one by one after shooting them three times. Then once all robots are dead in this section, the wall will go down and you should head to the next room. Final boss cannot be one shotted.