More than a year after this I finally decided to give it a real go, finished it yesterday on Normal and I'm rather happy with the time investment (hence the bump).
It is a good game, takes a bit getting used to as it is not necessarily your typical shmup. In particular the problem I mentioned months ago (see above) with all the explosions takes a bit of getting used to and in games like these I prefer less fancy stuff for playability over style.
It reminded me a lot of the classic PC shmups like Raptor (although this is a side-scroller/horizontal whereas Raptor is top-down/vertical).
Ivo.