Not bad at all. Very engaging at all points of time. Very casual, very retro, very easy to pick up and play at any time. The progress of difficulty in this game is quite balance and most new levels offer new challenges. I liked the way bosses are designed, reminds me of contra's crazy bosses. Would be even better if power-ups give more visual aesthetic and I have more weapons of choice available at my disposal and I can switch them out at will.