Sesame Street: Elmo's Letter Adventure for the N64

Many have been said but it goes like this

The entire DBZ series on PS1/2 minus Sagas
Yu Gi Oh Duelest of the Roses
Hey You Pikachu (would not play that game with others in the house)
Though not quite so "in the closet" I used to play the Pokemon TCG on GBC a lot and finally have a new copy of the game which I might pick up again.

I could name off a list of terrible Genesis and SNES games too like this one Taz! The Tasmanian devil game on Sega Gen, horrible game but I played it to death.

There's some really bad PS1 games like WCW Thunder but I loved them back in the day.

Also Power Rangers on the Sega CD, Power Rangers tournament fighters on the SNES, and one other Power Rangers game on the PC (some point and click adventure), I could not get enough.

This. I bought Dead or Alive Xtreme 2 for the same reason everyone else did. However, after actually playing the game, I felt it was much more than just eye candy.

Im hooked on Animal Crossing...

Well I loved Monster Ranchers on Ps1.
But for my Ps2-Ps3 era...
Guitar Hero

*scratches head*

well I liked Lair.