Heretic

The Good
Raven introduced here some interesting gizmos to the game - you can look up and down and fly. There's also an inventory, so you can carry with you some magical items, for example:

• quartz flasks, which heal you
• tomes of power, which make weapons work in a different way
• morph ovums, which turn your enemies into chickens (and you, if you're not careful)
• and torches, rings of invulnerability, and more.

Unlike Doom, Heretic has more detailed plot, however in the end it comes to "one-against-everybody" scheme. This time you will massacre monsters in caves, medieval castles and underwater fortress. They are varied - you'll encounter golems, wizards, gargoyles, ophidians (half snake, half human) and undead knights.

Music is brilliant (however not so brilliant as in Hexen), it's scary and gripping. My personal favourites are tracks from E1M4 and E2M4. Map design and graphics are as good as those from Doom.

The Bad
It's sometimes too similar to Doom - most of weapons are just repainted Doom weapons, and gameplay is almost unchanged - you run through rooms fulfilled with monsters and from time to time you search for keys. Also, multiplayer is the same as in Doom - only cooperative and deathmatch are present here.

The Bottom Line
Most of people look upon Heretic as modification of Doom. However, it won't hurt to play. Today you can download a source port which can add 3D models and hi-res textures, so the game will be much more enjoyable.