Ages ago, I got my Game Boy. Tetris didn't exactly get me hooked (but did get my father hooked), so I got more games. At the time, I very much liked platformer games. (I was a kid, after all). So I got TMNT:FotFC, SML, SML2... and a few years later, I was completely sick of platformers and didn't do much with my GB. My sister asked to borrow the GB to her, later she got into Pokemon and got a GBC, and then I got into Pokemon and got my GB back - and later got a GBA and that got me again interested of mobile gaming with its wide variety of actually interesting games! =)
But among the platformers I played back in the day, I thought SML2 was the coolest one. And, since I was a hopeless victim of TMNT marketing (I got over of it), I got TMNT games for GB and actually liked them.
And, actually, of the games I owned, TMNT2 was probably the best and most exciting game overall.
TMNT2 - or, as its full title goes - Teenage Mutant Ninja Turtles: Back from the Sewers - is, as mentioned, a platformer game. However, it is not completely a platformer game. Some of the levels also allow the user to move in depth direction (a la TMNT2 on NES or the TMNT arcade game); There are also some levels that have forced scrolling, and this is where the depth rules.
The gameplay was simple enough. You got through the levels, beated the minibosses in the end of the levels, and prepared for the final fight. In the end of the levels, you had two possibilities: If any of your four turtles got "captured" by the enemy (that is, killed), you fought a guard robot and had the chance to get one of them free. This fight was pretty dull because if I crouched at correct spot and whacked the button I won it every time well before the time ran out. If all turtles survived through the level, though, you could get to a pizza bonus game...
I believe the graphics were much better than in the first TMNT GB game! In the first game, the artists had no clue, really, but second game has a little bit more cartoonsy style, more accurate depiction of the main characters, and I believe this was the first game I had that also used dithering beautifully, doubling the 4-grayscale palette!
Some graphics were pretty odd, though. Some intentionally, some not. The intentional silliness was pretty fun: Falling in the sewer on first level showed eyes in the sewer, and a speech bubble "Who put the lights out?" (joke from the arcade game, I believe); Some graphics were just odd (The options screen was titled "Teenage Mutant Ninja OPTIONS", and I think Shredder had the habit of taunting the user with his huge thumb...)
The sounds were pretty good, too; The music was absolutely great, definitely the best music I ever heard on GB, and it wasn't even "TMNT-specific" (apart of the main theme); the game even had a "BGM test" option in the option menu. The game was the only one I had that used samples, thought this was one of the most comical ones; The levels started with a sample that had a somewhat noticeable accent. "KAWABANGA!" =)
Oh, and the odd thing I noted later on: I think I got the American version of the game...
My judgement: It was a very entertaining game, even now.
Released by Konami in 1992.