Reading so many negative comments about the howlers and the weapons is actually ridiculous. :D Why is it that these days every time players face a challenging, unique and smart enemy type they instantly shout "bad design"?
Come on, you can't be that bad, you just have to get used to them, once you figure out how the howlers move and learn how to shoot them in the head they'll be no problem. Actually figuring them out was one of the most fun parts of the game for me.
I'm not sure I'd describe an enemy that runs up to the player and jumps at them as "challenging, unique and smart." Use the stone to knock them back when they get to close, and murder them with your regenerating magic. Repeat eighty thousand times because the early game has basically no enemy variety. I like the game more than Fenixp seems to (I recommended it to someone or other on these forums), but I can still admit its flaws.
You have a million ways to kill a Howler. You can combine the stone with ectoplasm which is great at the beginning of the game because the stone amplifies your magic and you can push them back with it but it's not the most effective way to deal with them later on when their numbers increase. If your aim is fine you can basically one-shot them with the pistol even on nightmare difficulty and if you combine that with the occasional ectoplasm you can deal with them in no time. The ice gun is also very useful because it slows them down so combining that with ectoplasm can also be a good idea. After you get the scythe and find the armor spell that becomes the best combination: the scythe is very useful because you can chop down their heads with it and if you use its alternate attack mode it also regenerates your health depending on how many enemies you've struck down with it. Anyway by the end of the game you'll just kill them with exploding skulls. :D
As to why I've said that the howlers are unique, smart and a very good enemy design in general: first they have two attacks (as most of the enemies in the game) which was not a very common thing back in the day. Their jump attack is very hard to dodge at the beginning because it has an insane range and their bite punishes those who don't deal with them fast enough when they are close and both of those attacks can deal a very high amount of damage depending on how badly they got you. I found this a very good design because they also have a very clear weakness: if they miss their jump attack they suddenly become very vulnerable (great opportunity to shoot them in the head). they also move in a very unusual, animal-like fashion which makes it realtively hard to deliver headshots from a long range but if you really want to be fast and efficient in the game that's exactly what you have to do.
They were considered very smart at the time because they behave like animals: if there are more of them they usually attack in packs and if you meet with only one howler, do some serious damage and it manages to escape there are some instances when it will alert other nearby howlers, regroups with them and attacks you.
Overall I think Undying is a very good game design because it encourages exploration and wants you to find those hidden amplifiers, mana wells and mana boosters. It's basically a powerup item based RPG deep down. It also wants you to experiment with the different magic-weapon combinations and spells, in other ways: it wants you to be resourceful. I remember that back in the day people complained how hard the skeletons were to defeat because they are very bulletspongy but if you were smart you could one shot them with the Invoke spell which makes them disintegrate (also using Invoke on human enemies makes them commit suicide) . The cro magnons at the end of the game work in a bit of the same fashion: they are hard to deal with until you find out that you can combine your lighting spell with the speargun and if you hit an enemy with the spear out in the open a huge lighting comes down from the sky and kills it in one hit.
You're right, the game lacks enemy variety in the beginning just like most FPSes of the time (remember the first few levels of No One Lives Forever, arguably the best FPS ever made? They were bad.), however at least you have 3 types of howlers.
As for the difficulty curve: if you want to prevent the game from becoming too easy on the later levels when you have more stuff to deal with everything, play on Nightmare difficulty, that will shut you up. :D