I would recommend against the PS1 versions of the Lunar games. If you've played the real versions (the original Sega CD versions) then the PS1 versions will feel cheap because of how fundamentally broken they are. The developers thought they were clever, but ended up destroying the gameplay. Neither are all that fun when compared to the originals. In Lunar 1, it's virtually impossible to gain a strength advantage since the bosses level-scale with you (this is CHEATING), and in Lunar 2, the enemies are horribly unbalanced (it is not uncommon to get killed with FULL HEALTH with a SINGLE ENEMY ATTACK within the first few battles of the game...complete bullshit). I didn't play the second one long enough to even get into it as the bullshit factor made me take it right back to the store. I still own the first one though, but probably only because the cover art has a shot of Althena's butt.
In any event, if the terrible gameplay doesn't drive you nuts, the badly used samples WILL drive you nuts; Nash constantly saying "Check this out!" always made me want to drive an ice pick through the TV.
I can't really recommend any good 2D games since I don't think I own any (yes, I own Lunar, but I said GOOD 2D games). However, if you're looking for a pretty decent RPG, I recommend Parasite Eve. It's 3D but just barely (in sort of an early Resident Evil kind of way). But the game is pretty fun, or at least I think so. Hard to explain combat in the game; it's real-time in the sense that you can move around and dodge enemy attacks, but attacking is turn-based using a timer (AT, or Active Time). Your AT bar refills at various speeds depending on the weapon you're using (I prefer handguns since they're quite fast). The storyline is really weird, very sci-fi-ish, which I normally don't like but here it works. It's a nifty little modern-day RPG (set in 1997 in NYC) but it can be hard to find.
Of course, if you do driving games, pick up any Twisted Metal. User opinion is split about the "best version", some preferring the SingleTrac versions and some preferring the 989 Studios version. I personally prefer the latter (TM3 in particular, TM4 feels slightly uninspired); their versions were much nicer...looked better, controlled better, played better overall. TM2 is ultra-cheap and is the only stain on the PS1's Twisted Metal franchise.
