Final Fantasy VII
Metal Gear Solid
Resident Evil 3

Can't go wrong with these bad boys, my top 3 games of ALL TIME.

Castlevania: Symphony of the Night hands down

You only have the following options:

1) You haven't played MGS1

2) You haven't played MGS2 and/or MGS3

2) You have a terrible memory

3) You are blatantly lying for some reason

Castlevania Symphony of the Night ( the best Castlevania ever! ) or Final Fantasy IX. Those 2 are the greatest on the PS1,no doubt. I'd personally go with Symphony of the Night though .

I've played all three, and what I meant is they are all far more similar to each other than MGS4 (which was a pretty large departure) incase that was the only one he had played.  In 1,2 & 3 you hide in a spot, watch enemy patrol patterns, make your move, repeat.  Yes some games added more elements (MGS3 camo system for example) but it all really boils down to the same thing.

Castlevania: Symphony of the Night. I never owned the psx version but I've played and beaten it on xbla and it's great.

I've been mostly disappointed with PS One classics. Like some users said before, they're too old. Most annoying thing aren't even the graphics, but the gameplay mechanics.
Jump'n'Runs were mostly satisfying though.
I'd recommend you Crash 2 or 3 (the first one isn't as good) or both Abe's Odyssey and Abe's Exoddus. Crash Team Racing and Kula World were good too.

I've also played MGS, Syphon Filter, Medievil, Driver, Rayman, Soul Reaver, Final Fantasy VIII, and a lot of big names from then (mostly as PSN Plus gift), and was disappointed of all of them.

You should definitely check Tomba/Tombi. It's a game that will forever remain a happy memory from my childhood. I'm not sure if Tomba/Tombi 2 is on PSN but if it is, it's another must check. Hmmm... I might actually go ahead and download the first one now that you reminded me of it with this thread.

I've owned it more than a year?

Why is this thread still going, I was quite sure I ended it?

OMG first I thought you mean Tomb Raider. Please avoid any 3D adventures or shooters. They aged very badly and are a pain in the ass now.