This is hard because I love the games for different reasons so they all serve their purpose and I love them for that purpose not overall...but I'll have a go.
1. Final Fantasy VII
2. Crash Bandicoot 2
3. Twisted Metal 2: World Tour
4. Final Fantasy VIII
5. Tekken 3
So many great games on PS1 but the top 4 I keep playing over and over, even now.
Hmm, pie.