The different scoring systems/play mechanics that some games have tried... I am ALL FOR experimentation and variety, I just wish that they always included an "old skool" mode for curmudgeons like ourselves. I agree that it is too easy to throw out "gimmick" as a cheap insult 
Nothing ever gonna beat Ol skool thats why we love it but these games are not " gimmicky " the each have a style of play and Ikaruga is a stand alone style original is not gimmick. Was the Holy Ys Book 1 an 2 Gimmicky when we all ran headfirst in to our first enemy to kill them instead of swinging a sword? cameras on consoles is a gimmick not a specific or altered style of gameplay. I love my old school SHUMPS to death but i love the rush i get off dodging a bullet frenzy with out bombs its fun to push ur self like playing Gears o war 2 horde mode on nightmare difficulty by yo self (in the dark).
Yes, I agree. As I said, it is too easy throw out the term "gimmick" as a cheap insult. So I won't.
I just wish there was more variety in the shoot-em-up genre. Back in the day, bullet-hell was a refreshing new play mechanic for shoot-em-ups. It breathed life into the genre.
But bullet-hell has been the convention for quite a long time now, and I wish we would see something *brand new* or some *revisits* to the past (updated, of course, in refreshing new ways).
For example, where is my GYRUSS 2010? I would love at least two modes of play: (1) the old game, refreshed with pretty graphics, and (2) a re-inventing of Gyruss that goes somewhere new... (I don't know, but I am trying to figure out how Gyruss + vertical scrolling shooter could be hybridized. Perhaps that isn't possible, but I still want Gyruss to be re-invented).
Anyway.