It is time for one. It is too difficult to find a list that doesn't include only 10 or 25 entries or ignore the more niche titles. We want the good games on PSN. Yes, all of the good games, old and new.
Once we get a good list of entries together, I'll categorize them by genre, link some youtube vids and maybe even add prices and more short descriptions.
Here's a couple I can recommend:
Hard Corps: Uprising - If tough as nails run-and-gun games are your thing, you should already know this one. Developed by Arc System Works, this is a 2.5D side scrolling shooter in the vein of Contra. It is retro as can be, and is a blast to play with a friend.
Galaga Legions DX - Unlike most shooters and previous Galaga games, this one has a more tactical and puzzle-like game play style. Your main objective is to shoot the bombs and squad leaders amongst the swarms of enemies as they sweep across the screen in mesmerizing patterns, then watch the pretty explosions as they are vaporized. Addicting and very good looking.
Keep in mind I have yet to play a vast amount of the PSN games so I will rely heavily on your collaboration.