Wololo wrote:I'm going to try Indiana Jones and the Fountain of Youth (although I wish the full game was available already...)
A lot of people have wished that for about 7 years now

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This also seems very promising. A demo is available too.
Wololo wrote:I was also a big fan of Gabriel Knight...any game suggestion in the horror/detective genre?
That was an awesome game, actually it is the only Sierra adventure that I really like. I am a Lucasarts fanboy.
A recent detective/future-noir gem is
Gemini Rue. Well worth the price, you should check out the demo. It runs fine on the PSP for the most part except that the rain effects are missing and the shooting segments can get tricky because there is some slowdown. It is perfectly doable though once you get the hang of it.
These games don't run with the PSP engine because they are compiled with older AGS versions, but:
One of the more long-running detective series is
Ben Jordan: Paranormal Investigator. The creator obviously grew in ability as the series went along, so the later games are more graphically polished and longer. But there exist reworked "deluxe" editions of the early games too.
As for horror games, you might want to check the
Chzo Mythos games by Yahtzee (yes, the Zero Punctuation fellow) starting with 5 days a stranger, then 7 days a skeptic, Trilby's Notes and finally 6 days a sacrifice. Trilby's Notes is the highlight of the series.
I haven't played them yet, but the
Technobabylon series could also be of interest to you.