For those who aren't in the know, Bug Princess became fairly notorious on the internet for having "the hardest boss in all of video games" in this video.
The phone version is basically the first game scaled down to work on a mobile device. It also comes with all these weird leveling systems that are a bit shit but it doesn't really tarnish the overall experience. There's also a multiplayer mode where you can connect with a friend or random to compete for score and whoever has the highest score at the end steals the other persons rewards, it's pretty cool. The leader boards also offer prizes for people who rank high up at the end of every week so there are lots of chances to get the games various currencies without actually spending a penny.
Last time I played a shmup on a mobile device it controlled like complete bollocks but this one actually plays pretty well. There's a dedicated area at the bottom of the screen for moving yourself around but moving out of it doesn't prevent you from controlling your character. There are two transparent buttons on the side that let you switch between the shot mode and beam mode for you ship as well as use your bombs. Each character also has a unique skill that can be used by double tapping the screen which is a nice little touch since the ability comes online quite often.
It's not exactly what I'd call a perfect shmup and I imagine a lot of people who are hardcore on the genre may turn their nose up at something like this. However, for me and my long train commutes to work, Bug Princess Duel is a nice little change from all the match 3/monster breeding puzzle games on the app store. If you're looking for a quick dose of shmuppy goodness for your train rides or to kill time with, the Bug Princess is pretty good considering it costs 0 money.