1: Streets of Rage 2. Never have like Street Fighter, no matter how many Turbo Alpha Pluses they shove in front of it.
2: Sonic. Mario may be the more challenging game, and the one I've played the longest, but nothing beats the speed feeling of Sonic.
3: Chrono Trigger. Probably the best RPG for the SNES (probably), plus Shining Force 2 > Shining Force
4: Gunstar Heroes. No brainer here, best two-player game in exsistence. Totally worth hunching around a keyboard with your drunk friend even if it's clocking in the years.