Since I am a douche who wants attention... Why shouldn't I post my o(pi)nion to and yell at everybody who doesn't agree to me... But humor aside, heres my list:
#5. Spongebob Squarepants: Battle for Bikini Bottom (Sony PS2)
It may seem odd that I am a fan of this show, but I LOVED it. As much as I loved the show I love this game. It's huge world containing lots and lots of references to the show (e.g. the candy bar bus scene in "Rock Bottom" or Sand Mountain). It's characters represent the spirit of the show perfect and the original voice actors sound great. All in all, I like it and everybody should check it out at least once.
#4. Contra Hard Corps (Sega Mega Drive/Genesis)
You know the drill, kill them all while shooting your gun in 8 directions. But this Contra is different. First of all, the game has a STORY! in which you can choose the outcoming. Also there are more levels than ever before, 16 in total to be exact. There are more (35 in total) and larger bosses than in any Contra before. The music is god-like and the visuals contain more than anybody would expect from the Genesis (effects contain even Sprite-rotation, something the SNES could NOT handle). Generally the game is way more fast-paced and rad than the other Contra games and it has still a special place in my heart.
#3. Virtua Racing (Sega Mega Drive/Genesis)
Actually this isn't that great of a game but I'm still putting this on the list because of memories. Me and my friends and siblings has SO much fun playing is back in the day and even today we play this game when we meet. Also it's very interessting because of the SVP in it.
#2. Megaman: The Wily Wars/ Rockman: Mega World (Sega Mega Drive/Genesis)
I love the Genesis, I love Rockman. It's both in one and I LOVE IT! It's basicly Rockman 1, 2 and 3 in one cartridge. Take out the passwords, put a battery in and create a Genesis-exlusive episode containing all of the gimmics of these games, include it and you got this game. It's features all that was great in the three first Rockman titles and updates it with Genesis grafics and music. Also unlike Rockman 7 this game conatins the "old" classic-Rockman design what is notable, considering Rockman 8 promos already established the Rockman 7 styled classic-Rockman design.
#1. Sonic CD and S3&K (Sega Mega Drive/Genesis and Sega CD/Mega CD)
Actually this would be cheating but I couldn't decide which one is better. S3&K has great visuals, lots of creative levels and incredible music.
SonicCD on the other hand has too great music (I was lucky to live in Europe), incredible visuals and innovative bosses. Also the time travelling idea showcases so many different art styles in this one game. A large number of very nice gimmics are present in all over the game and i love them.
If you really want me to choose then I'd pick SCD. It's music and level design is (in my opinion) greater than anything before.
Other games I love but I couldn't fit on this list are: the GTA series (especially from 3 to VCS), Street Fighter 2:SCE, Zero Tolerance, Gran Turismo series (especially 3, Concept and 4) and the Streets of Rage/ Bare Knuckle series.