I only have RR and Lumines. Other games, I really wasn't sure were worth the plunge without at least seeing them first, and I'm generally not a big fan of importing when I know all those games will be available here fairly soon, and localized. I've based these putchases on tons of impressions from other people and my tastes in games in general.
I can tell you what some other (generally trustworthy) people said about the games you mentioned:
Dark Stalkers is definitely a high quality game, marred only by slow loading times (often compared to load times of Capcom fighters on PS1), which I've heard can get annoying when you are in the matches that last for a short amount of time. Other than that, it's been said to be a perfect port of an arcade game, and just a very good game in general if you like 2D fighters (I'm not a big fan of the genre though).
Metal Gear Acid is not very import friendly as it has large amounts of Japanese text, but is apparently a very good turn based strategy game (again, I'm not into that genre at all) that takes around 25 hours to complete. Graphics are worse than MGS2 on PS2, but much better than MGS on PS1.
The Hot Shots Golf is from what I understand much like the PS2 version, even has the same graphics quality (also, better image quality than the PS2 version) This, with RR is probably the most technically visually impressive game on PSP right now. It's wireless multiplayer mode allows people to play together, without taking turns and track each other's progress to see who completes the course first. I would love to play this, but again, I've read it's not very import friendly (all the menus and texts are in Japanese), so I'll wait for localized version.
Dynasty Warriors features the same crazy battles against tons of soldiers as the PS2 versions, but to make the game more short-burst-gaming friendly, they've split the maps into smaller segments, so when you get into a new segment, you can start the game from there next time. I've been told that if you like PS2 version of this game (I don't like them at all) you're going to like this a lot. The graphics look simillar to PS2 versions, but polygon counts on solidiers are downgraded. Personally, I find even PS2 versions of this game to be really poor looking, so I'm not very enthused about the looks of this on PSP. The good thing is that they preserved all the massive numbers of enemies you fight against, and the gameplay in general.