I think vertical orientation is my fav, though it depends on the game. I enjoy both simple retro arcade style single screen as well as scrollers with continuous barrages of enemies. I agree terrains get in the way of horizontal shooters. I already have to dodge bullets and enemies; don't make me dodge static land masses, buildings, navigate narrow caves or other obstacles. Games like Blazing Lazers, Super Star Soldier are awesome due to their symmetry, openness, and the fact vertical orientation really puts you in the cockpit. If vertical shooters had one disadvantage, it's that you can't rotate that sweet widescreen on it's side and play them upright with an extended playfield.
But I also have a soft spot for Cute-Em-Ups. Parodius I am a huge fan and own all three Super Famicom titles. Am I allowed to say that here? Air Zonk, Magical Chase are also great despite being all horizontal. It's really all about mechanics, pacing, enemy density, and making good use of screen space.
As for usage of the word SHMUP, I rather use it than shooter, because when someone says shooter, people immediately think fps dual stick type stuff. I loathe that crap. In the same way, beatemups (1 vs world) is a distintive genre from fighters (1 vs 1). Shootie just sounds dumb, and I've never heard that term before, but I don't keep up with twatter and facepalm. I bet a millenial coined it. Sounds like something a Justin Beiber or Miley Sirus would say...
Regardless, I'm quite fond of the way Shmup rolls off my tougue when pronounced phonetically. Not many English words combine the sh and m constanants, but it works!
