It certainly is a crudely stuck-together hybrid of the two games which, in truth, were already very similar. I was unaware of this fact as a kid, but I can just about accept most of the hacked-on Gaiden parts of the game. It still works as a whole ... for the most part.
The first thing I remember appreciating was the developer ditching the annoying timer. For who knows what reason, all three console-based Ninja Gaiden games had that annoying timer. It's a video game mechanic that stopped me dead in my tracks, not wanting to replay those games for years. If only because it was significantly less frustrating, I enjoyed Shadow of the Ninja more than the critically acclaimed Ninja Gaiden series.
The given lives and continue system seems fair, but still challenging to the player. The difficulty level is thankfully still Shadow of the Ninja based, which was a bit less about twitchy speed play and more about cleverly timed strategies. It's certainly sympathetic to a smaller, less detailed screen.
The game's graphics and animations are both console faithful and rich in life and ideas. They really make use of every bit of the Game Boy's limited palette of mono shaded effects. The soundtrack is also spectacular, unparalleled back in the day. It should be held up in chirpy chiptune heaven near Mega Man 2.
Level design is also something they got right, and playable character Ryu has many things to jump, grapple, hang and rain down swishy knife hell from. On a negative note, Special skills have been limited to just a single fiery one. Although disappointing, this ability is effective enough. The boss designs are worth a mention. The big guy/tiny guy duo at stage two's end is genius, with the little guy trying to grab your legs to slow you down while the big brute strides over to give you for a good old fashioned kicking!
Now if you're really going to go for it and make a proper Ninja Gaiden game, what should not be left out? Well an over the top graphic story for one thing. Knowing the fans would want it, the developers added a paper-thin story presented only briefly. Sadly, the thrown together cinemas only add to the tainted and hacked-together nature of it all. Precious little of those impressive shifty eyed cut scenes are here folks, just enough of a sci-fi premise to hold the game together. It's a shame as a great deal of the cinematic tension has been lost ... but the Game Boy can never really lay claim to any vast story arc's and epic yarn's outside of the role-playing realm.
Even though it doesn't match the heights of either console franchise, Ninja Gaiden Shadow is still worth playing through. It's worth checking out just to see how each part was sewn together, especially given the shady circumstances over its birth. Rest in peace, Hayate and Kaede.