Hmm well without knowing what the others games are on there (maybe list them?)

Here are some different types of games I owned when I was young that I thought were good.

Vectorman 1 &2 (side scrolling shooter)

Toejam and Earl 1 &2 (first one was kind of exploring game, the second was more of a traditional platformer)

Adventures of Batman and Robin (Contra-esque game; stupid hard but the music is excellent)

Golden-Axe (hack-n-slash goodness)

Shining in the Darkness (first-person dungeon crawler turn-based RPG, that I was never able to beat)

Can't really remember anymore other than that there is the Sonic games you said are there already.

Earthworm Jim 1 & 2
Ultimate Mortal Kombat 3 (first time Noob and Rain were ever playable)
Mortal Kombat 3 (Secret 8-character Endurance Mode in Vs)
Aladdin
I really didn't play many games on that system. Meh, you have the Sonic titles, so it's good enough.

You might want to try this: Complex Gaming - Top 100 Sega Genesis games

Yeah, I guess I should list them:
(liked games marked with dot-thingy)
Alex Kidd
Altered Beast
Alien Storm
Arrow Flash
Bonanza Bros.
Chakan
Columns
Columns III
Comix Zone
Crack Down
Decap Attack
Dr. Robotnik's Mean Bean Machine
Ecco
Ecco II
Ecco Jr.
Eswat
Eternal Champions
Fatal Labyrinth
Flicky
Gain Ground (listed twice, for some reason)
Golden Axe II*
Golden Axe III*
Jewel Master
Kid Chameleon
Ristar
Shadow Dancer
Shinobi
Streets of Rage
Streets of Rage 2
Streets of Rage 3
Sonic the Hedgehog*
Sonic the Hedgehog 2*
Sonic & Knuckles*
Sonic 3D*
Sonic the Hedgehog Spinball*
The Ooze
Vectorman*
Vectorman 2*
Virtual Fighter 2

The other 40 are non-Sega games. I completely forgot I had Golden Axe, awesome game it is.

I suppose Sonic 3 then, because Sonic 3 and Sonic & Knuckles can combine, and were originally supposed to be one game.

I have really appreciated the Streets of Rage series, Vectorman, Comix Zone, Collumns, Dr. Robotnik's Bean Machine (although the game is surprisingly challenging) and of course, the Sonic Series with the exception of 3D Blast. I get what they were trying to do with the game but honestly, it didn't work whatsoever and I could never get passed the third zone.

So... I may have slightly misread the first post, especially regarding the "installed on the system" bit, and I must ask

Is it just Sonic & Knuckles, or Sonic 3 & Knuckles? If it's the former, then I don't think you can lock the two together, because you'd need a physical copy of S&K and S3 (I think, if there's some sort of lock in option or something then that's pretty awesome). If it's the latter, disregard my previous post with extreme prejudice.

Also I agree about Comix Zone

Gonna throw out some of my faves. Sorry about the repeats.

Aladdin
Bio-Hazard Battle
Castlevania: Bloodlines
Comix Zone
Contra Hard Corps
Fatal Labyrinth
Gain Ground
Hulk
Kid Chameleon
Micro Machines
NBA Jam
Phantom 2040
Shinobi II
Shinobi III
Shadow Dancer
Shining in the Darkness
Shining Force 1 & 2
Space Harrier 2
Splatterhouse 2 & 3
Streets of Rage 1, 2 & 3
Vapor Trail
X-Men 2

I also seen this built in game Sega in a dollar store circular for like....35 or 40$.Is it possible to insert cartridges into it or can you only play the games built in the hard drive?

Streets of Rage 1-3 are pretty amazing as are the Golden Axe games. I'd seriously suggest the Vectorman titles as well. There really are an amazing selection of games for the Genesis but I feel like I'm just restating stuff that others have already said.

I see you have the Ecco games. Play them (well I never played Jr). They're excellent.

Also, I don't know if it's actually considered a good game, but when I was little I had the game Valis. It's a fun side-scrolling beat 'em up with some stupid story idek. My mom bought it for me because it has a female hero.

Also, play the game starring the Seven-Up Dot if you can. :D

They make them to take cartridges, but I've heard rumors that some games don't work and they can even potentially damage the cart. Not sure if that's true, but it always put me off.

This. Sonic 3 and Sonic & Knuckles, when combined, are hands down the best Genesis game. I still go back to it after all these years.

Yeah, pretty much what everyone else said.

My personal favorites were:

The Disney platformers: Honestly, these all well made games. From Aladdin to Lion King, Castle of Illusion etc. I enjoyed them all. Plus, they're all a bit more challenging then they first appear.

Ecco the Dolphin and Ecco the Dolphin 2: Very well made games. These were freakin gorgeous back in the day. Plus, I always loved surfacing in that game. Not sure why.

Altered Beast: It always seems to make "worst of" lists, yet I thoroughly enjoyed it.

Mortal Kombat, MK2, UMK3 (well yeah, of course).

Streets of Rage 2 and 3. The first one was alright, but not nearly as good as the second and third titles. Just my opinion though.

Golden Axe series: Played these for more hours than I'd care to admit.

X-Men and X-Men 2: Neither held my attention as much as they should have, but they were well made games.

Strider: Loved this game, even if I was terrible at it.

Eternal Champions: This game is a lot harder than I remember it being back in the day, but it's still one of my favorites. Xavier FTW!

Weaponlord: Another fighter from that era. Kind of a cross between MK and Street Fighter. More cartoony, but still violent. I always dug it.

I'm sure that I could think of more, but there are a bunch of lists on here already. Lot's of good ones out there!

I always loved Decap Attack. One of my first Genesis games.

Here are a handful of SEGA Genesis titles that I don't think have been mentioned, but have always been some of my favorites:

Desert Strike: Return to the Gulf
Great Waldo Search, The
Jungle Strike
Jurassic Park
Lion King
Mega Bomberman
Paperboy
Primal Rage
Road Rash
Simpsons, The: Bart vs. the Space Mutants
Skitchin'

I know that you're not looking for sports titles, but NBA Jam Tournament Edition is a must-have for any SEGA Genesis fan. You're also able to play as unlockable MK characters, so there's that.

It seems the games I already have are good ones, I guess I'll give them a shot.

I also a lot of suggestions for Disney games, which I will probably get The Lion King before anything else, and X-Men games, which I didn't even know were on Genesis.

I shall see to these fabulous suggestions and adhere to any more. Thanks, guys.

For the Sonic and Knuckles game, if you have it that is, attach it to some other game and you can play the one of a million different Blue Spheres levels.

I got a kick out of that.

Batman Returns
Final Fight
Golden Axe
Jurassic Park
Maximum Carnage
Rock n' Roll Racing
Sonic 2

Kid Chameleon is seriously under rated in my opinion.

A few that some forgot to mention:


Battletoads
Boogerman
Captain America & The Avengers
Cosmic Carnage
Dick Tracy
Death And Return of Superman
Ghouls N Ghost
Judge Dredd
Phantasy Star Collection
Prince of Persia
Rocket Knight Adventures
Sparkster: Rocket Knight 2
Teenage Mutant Ninja Turtles: The Hyperstone Heist
All Mortal Kombat games

Shaq Fu is the only game that you'll ever need. Srsly.