Despite the generic name, S.H.M.U.P. is not a generic shmup. A finalist at the Chinese IGF, it is indeed a horizontally-scrolling shmup, but with some unusual characteristics.
Killing enemies gives you points you can use to upgrade, a common trope, but upgrades persist the next time you play under the same username, even if you've died. Indeed, it's designed so that you will almost certainly lose the first time you play, but that over time (a few hours of gameplay, at any rate) you will build up enough to be able to persist and triumph even through the higher, and more difficult, levels.
Control is entirely with the mouse; your cluster of ships follow the mouse pointer around. Right-click launches missiles, of which you have a limited supply. There's a boss at the end of each level, but these are not all that impressive.
Behind you are a cluster of squares that you can think of as akin either to the cities of Space Invaders or the points you must protect in a tower-defense game. Ships you fail to kill as they scroll by reduce them, and you can lose either by losing them all or losing all your ships.
However, at higher levels, enemies self-organize into impressive opposing formations -- sometimes taking advantage of combined arms, with defensive ships protecting high-fire but more vulnerable ones, sometimes organizing into megaships, in the fashion of amoebas forming into the cells of a multicellular monstrosity.
Gameplay is not, however, particularly challenging from a traditional shmup perspective; at worst, you simply die a lot, build up points to buy upgrades, and eventually triumph even with a fairly minimal twitch-action skill set. There would seem to be a bit of a casual game influence in this.
High scores can be posted to your Twitter feed, something I haven't seen before.
In general, it is neither the most visually beautiful shmup, in a genre known for its weird psychedelic beauty, nor the most challenging game of its type, but there are some interesting design ideas here.