You don't have to Take Our Word for It. The entire soundtrack for the Amiga versions of the second and third game can be legally downloaded for free at Tim Wright's homepage - including at least one unused theme for the second game.
It's Short, So It Sucks: While it's around the same length as the first two games, the decrease in Nintendo Hard and structure changes (levels as opposed to a pseudo-open world), resulted in this being one of the primary criticisms among reviewers for the third game.
Nightmare Fuel: Some of the Beasts you face are extremely freaky looking or just plain wrong (like a being who is visibly beheaded yet moves as if this were its natural state).
Porting Disaster: The US Genesis port of the first game. The developers didn't bother to account for the difference between NTSC and PAL formats, causing the game to run at a ridiculous speed. Needless to say, the difficulty also skyrocketed.
Many versions of the first game actually manage to avoid this. The basic idea and gameplay were quite simple and despite the downgraded graphics and/or music in many platforms the gameplay was often quite good, when compared to the original Amiga version. Apparently the issue in the American Genesis/Megadrive release was fixed for Japanese release. The latter has also upgraded graphics (closer to those used in PC Engine/Turbografx-16 release) and different ending sequence. However, non-Amiga versions tend to lack some individual tunes from the soundtrack when compared to the Amiga version. This applies even to the version for PC Engine/Turbografx-16 despite being on CD and using audio tracks for music (and possibly to the FM-Towns version, which supposedly uses the same CD soundtrack as PCE/T-16 version). Surprisingly many versions manage to include the parallax scrolling in the overworld sections. Even the one for ZX Spectrum, which was not known for its scrolling capabilitiesnote The version for Amstrad CPC could have done better, though.
That One Puzzle: The third game has the slab puzzle in the Caves of Bidhur; every other puzzle can be solved consistently, but this essentially involves approximating a physics puzzle in a game without physics. You have to get a large slab across a long (but shallow) pit by placing (and moving them as you shift the slab along) three balls in said pit correctly so they evenly balance the slab correctly, one mistake and it falls in the pit and you have to go back to the last checkpoint. In itself this would only be kind of irritating, but the last checkpoint is at least a few minutes back and requires you to enter a cave full of respawning Goddamned Bats that you need to kill a certain amount of to get the hammer you need to do the slab puzzle, so you end up getting drained each time you screw up. Finally, there's a boss fight straight after solving the puzzle; while not too difficult it's another way to get sent back if you mess up and die (and also Nightmare Fuel if you run into it without being ready).