Sometimes the faces don't register that you've  clicked them for some reason, but I like the idea of target/distractor items and looking for the right one. In this particular case, you have one target numerous times and a distractor item. Since there's 1 of each, it's very easy for players to identify the one they need, and dismiss everything else. This leads to a very quite search because they are guiding their search to the item they need, and automatically processing out the other item. You can see the same sort of thing with colours. If a player has to look for blue items over red, the red will get filtered out. 

Have a think about how you can add challenge to this experience. Also once the player clicks all the faces, the game stops. There needs to be some sort of win screen or way to progress in the game. The score is nice, but the score in this case will always be the same for all players. Which means there's no highscore option for replayability. How can you modulate this? Maybe some sort of time attack that makes the player want to beat their own time?

An indication when you click all the smiley aliens  would be nice, as I felt like I missed one. Apart from that I liked it.

Interesting idea, but an end screen could be added once you have clicked on all the aliens (you could make it automatically switch to the win screen after a certain score has been reached.)

Once I finished with the objective the game stops and I cant seem to leave the game but other than that its a nice simple find and click game. 

When the game is finished there is no actual end screen or indicator to say you have either won or lost when the aliens have been clicked other than a score in the top left. Other than that I feel the game, with a bit more work, could become a lot better.