Hi, first post! Sorry that it's a long one :)
Like probably everyone here, I love DoomRL and I sometimes dream up other FavoriteGameRL ideas. In my mind, the first significant evolutionary step in the "doom clone" combat-based FPS genre was half-life, and the next was Halo. (I am not counting games with roleplaying elements like deus ex, system shock, ... in this genre). Halflife was awesome for its immersion, atmosphere, complex environments, AI, ... hard to implement in a roguelike. But I think the changes Halo made to the Doom formula can be applied to DoomRL to produce HaloRL.
So this is brainstorming HaloRL, I'd love to hear your ideas about gameplay mechanics, features, especially criticisms. I'm not promising to make this game myself or anything, so let's not get bogged down in technical worries. for this purpose, let's assume that I kidnapped Kornel's twin brother and am forcing him to write this for me. :) I made some concept art in PabloDraw and linked it below for discussion purposes. To my knowledge all these ideas are 100% original, but obviously I could be wrong.
So, combat would be DoomRL engine except for the recharging shield mechanic, only 2 weapons at a time, and grenades (including stickies). Visibility is line of sight to the edge of the screen. Big levels (particularly outdoor ones) would be multiple screens in size, as indicated by the pluses at the borders. You or the Elites can use vehicles, and you have friendlies (marines). There should be very rudimentary squad-based AI.
The most significant thing is the handling of 3D. Each level is composed of two Z-layers. On interior maps, the first level is the ground floor and the 2nd level is the second floor, while on exterior maps, the 2nd level is the sky. Importantly, the 2nd level is rendered as if the viewer was looking up, not down - hence the skybox showing the halo ring with some dynamic clouds and sun. Empty space is represented by _ and line of sight is calculated accordingly. % represent windows, which are broken after 1 damage.
The figures show grunts, Elites, Trees, ^rocks, marines, a warthog (with headlights), Ghosts, an alien dropship, Hunters, *sticky grenade, 0bodies. > is the stairs, but in this case it just means "to the second floor". The hero is @, and the same square on the other Z level is colored green so you can quickly see where you are.
I tried to respect all the line of sight rules etc when I made the art, but I probably made some mistakes. And, i think there is room for improvement in the colors and the skybox design. Which brings me to a question, does anybody run these games in an actual terminal? i.e. is 80x25 and limited color palette actually worth maintaining, or can we make 80x50 with more shades?