Overly-frustrating and cruel, 16-bit Diablo this is most certainly not.
In a nutshell, you play the part of a poorly-equipped wizard who must venture through a dungeon filled with traps and monsters, solving various "puzzles" and taking part in many downright annoying battles along the way. It looks good on paper, a Dungeons & Dragons-esque dungeon romp in isometric 3D sprites, with traps to outwit and foes to vanquish in an oft-gory manner. Despite being rather cheesy and cliched, the game could have actually worked fairly well, and could even have become an enjoyable Genesis RPG, with excellent graphics for its time.
So what went wrong?
My main gripe with The Immortal, as with many other games of the late 80's and early 90's, is that it's simply too difficult. The myriad of traps that litter the dungeon often involve pure luck to pass (such as the array of arrows shooting out from the walls), while others -- such as the pit traps or giant worms that spring out from the ground to consume our hero -- are often impossible to detect unless you've already played the game and fallen into the traps once before. It becomes more a roll of the dice and a memory game than involving any skill, as you try to get past the same traps over and over again.
Combat is similarly flawed, with an exceptionally simple combat system hidden by the use of large, colourful sprites and impressive death animations that involve exploding heads, mutilation, and a number of other gory ends. Despite these impressive graphics -- quite an achievement for the era -- the combat system relies heavily on luck, and involves practically no skill whatsoever.
The game isn't all bad; from a technical standpoint, the graphics and animations are impressive for their time, the dungeons are varied and complex, and it's rare to see a Genesis game exhibit such gratuitous acts of wanton violence -- certainly a selling point at the time. However, the entire experience is marred by the same thing that made Night Trap so flawed: It relies far too little on skill, and far too much on luck, and past experience of repeated failure.
Perhaps an achievement for its time, but by today's standards, the excessive gore is nothing new and many other emulated/retro games have more impressive graphics. Simply put, The Immortal was a flawed game when it was new, and it hasn't withstood the test of time very well at all. I'd only recommend this one to the most hardcore, dedicated players who crave a unique and extreme challenge -- for the rest of us, steer clear of this game.