ABA Games - I've pumped for ABA Games a few times in the ToJ forums but not in the CGA forums; ABA is old school 2D shoot 'em up like you remember w/ great action-based gameplay, kicking music and phosphorescent abstract graphics. Very addictive. (Torus Trooper, Parasec 47, Tukumi Fighters and rRootage are my faves)
Warning Forever - Similar to rRootage from ABA Games, this is a 2D shooter that's just boss battles. No stages, no power ups, just time-attack battle after battle with an evolving, mutating boss machine. I *think* there's an end boss once all 9 forms/attack types have evolved to their final stage, but I haven't been able to get that far.
Every Extend - (Tek already listed this above {OMEGA}, but I'll add my recommendation for this fantastic game) inovative 2D "exploding" shooter where you pilot a bomb on the screen and try to blow it up in a position that maximizes the amount of chain explosions you can create. Cause enough damage and you earn replacement bombs; otherwise, you'll run out. Deceptively simple in concept, the game is actually pretty deep once you get into it. Simple abstract 3D graphics and great soundtrack. It even includes a hidden boss (who is REALLY hard to beat).
Wirehang Redux - Simple coffee break game where you try to fling yourself sky ward using a wrist mounted grappeling hook. Maximize your velocity and points by flinging out the hook at the last possible second and to the highest point. Also addictive.
Icy Tower - Another simple addictive coffee game that involves simply jumping from one platform to another going up a tower. That's it. But the game's sound design and comboing system will keep you coming back. (I've also heard good things about "Super Monster Painter", on the same page, but haven't played it myself)
Super Mario Pac - Take sprites from SNES classic Super Mario World, a device from Mario Sunshine and gameplay from old school "jet pack" games and mix. Makes for a nice light retro break. Consume with cheetos.
The Spirit Engine - Fully-realized 2D sprite RPG with its own unique combat system, story line, characters and game world. Mixes magic, zombies, the old west, robots and shotgun toting priests all into the same world.
Splinter Source - Sam Fisher goes sprites! A 2D stealth game? Yup. Only one level here, so once you figure it out there's not much replay value, but the level has multiple solutions, just like the 3D version, so you can always go back and try another method.
Bontago - Sorta like Tetris and Jenga rolled together, and then given strategic elements. Stack random boxes on top of each other to build towers and create areas of control. The higher the tower, the larger the area you can control. Take over all of the control points on the board to win the game, but watch out for special boxes that cause earthquakes or explosions that can knock your unstable tower to the ground.
Cronberg/Bonobo - Video game version of a German tile-laying board game with heavy strategy elements. Again, simple concept, but deep gameplay.
More to come...
(RTS)