There are no two ways about it: this version of Tetris is special.
For one, there is a certain purity of form here. You can move, spin and drop your pieces. That's it. There's no fast drop and you can't spin your piece indefinitely to keep them from falling. You can slip pieces underneath holes but your ability to do so is limited. Your strategy has to be long term and take into account all possibilities because you only get to see what you're getting next and you can't swap a dropping piece for one in your queue or any of that nonsense. This is about as basic as Tetris gets and, while there are a lot of versions its equal in this regard, none have quite the tight, regular and responsive controls that this has.
In addition, the sound and visuals here are still quite charming to this day. The gritty, cheesy synth sounds the Game Boy is capable of are a perfect match for the green-and-other-shades-of-green graphics. These are both in term a perfect match for the Russian folk music sound of the soundtrack. Your rewards for a job well done are as simple as gameplay, either some Russian dancers or a rocket blasting off depending what mode you play in.
Speaking of modes, there are two for single players. A-type which is a classic marathon mode where you compete for high scores. Even w/ it's simplicity there are a few basic strategies you can take with varying effect on the final score. There are rewards for high scores but only two different ones and, honestly, the main appeal is just trying to do better and better each time--a good thing, in this case. In the he other mode, B-type, you try to get twenty five lines at a certain difficulty level and a certain amount of the game area already filled up. This is more of a bite-sized challenge for those times when you have only a few minutes but the higher levels are going to give most gamers fits trying to beat them. The actual gameplay and controls in these modes are identical but their differences provide you w/ a host of different strategies.
Two player mode is a real blast as well. You need two cartridges, two gameboys and a link cable to make it work, which is how everything was back then but since Tetris was a pack-in title, even today it is not a hard to find someone else who has a copy. The event was competitive where your lines dropped extra blocks on your opponent and vice versa. Since everyone plays Tetris and everyone thinks their strategy is superior, there is something extra satisfying about winning a two player game.
Really though, the strength of Tetris is in the solitary joy of trying to beat your own high score. The Game Boy version proves that all you need to build a legend is rock solid game play and a great concept. The rest is just finesse and this is a game that has it in spades.