Most of the time if a 2D game was also on Saturn, then the PS version sucks. The only exceptions to this I know of are In the Hunt and certain versions of Street Fighter II (Super and Super Turbo that are the second CD of the "SF Collection"). KOF 95 is, I'd say, "acceptable" on PS. But by the time KOF98 came out the PS ports were basically unplayable defective software. Pretty much the same for Capcom stuff, although one could make the case for either the PS or SS versions of SFZ3 since they are quite a bit different.
So I guess since you won't do anything 3D, you are looking for 2D games that are exclusive to PS, and actually good.
Hmm...
Rakugaki Showtime, Super Robot Wars Alpha (and Alpha Gaiden), the Gundam The Battle Master series (the best one is the US only release, "Gundam Battle Assault 2"), Gunners Heaven, Bomberman Land...um...DDR?
Hard to do, this. Most of my PS games are 3D. I quite like Love and Destroy, the Choro Q games, Kamen Rider (no, really), Slap Happy Rhythm Busters, Tobal 2, The Italian Job.