With some more work, you can really make this something great.

I found a couple bugs.

1. (which I tried to reproduce but had a hard time with it) On the first turn, I waited until the timer went to 0-5 and shot an grenade. The game said player twos time was up, and player 1 had a turn again.

2. This works for either turn. When the timer is almost up, if a grenade is thrown by for example player 1, and player 2 walks into it, it is no longer player 2's turn.

Perhaps you want to use a clamp for when the player launches their grenade, and keep the -0 from going below 0. Also, make a wait time, so the next player can't have their turn until the last players grenade has been blown up.

All in all, its fun and well designed. Not sure if anyone else has experience this but the sprites aren't either overlayed or have no alpha channels.