In my last post on enemies in Devil May Cry 4, I compared the new demons from DMC4 to a particular group of demons from Devil May Cry 3: the Hell reapers. In my opinion, the Hell reapers of DMC 3 are an exceptionally good group of regular enemies because they combined a solid theme shared among all of them while also being good at requiring the player to adapt his strategy depending on the composition of the enemy group.
First off, all of the 7 Hells type enemies share several features in common appearance wise: they all where hooded cloaks, they have a gaunt, skeletal appearance, and almost all of them use scythes. In essence, they are all look vaguely like the cliche Grim Reaper. At the same time, each individual type of Hell reaper has a very distinctive look, particularly in terms of coloration and posture. So, a large group of 7 Hells looks like a mob of similar, but distinct individuals. I think it works quite well.
More important to the success of 7 Hells as enemies is in how each individual type of Hell reaper has its own focus:
Hell Pride: The most basic kind of Hell reaper, these guys are only capable of short range melee attacks.
Hell Sloth: These Hell reapers are capable of teleporting, making them good at surprise attacks.
Hell Gluttony: These ones are capable of performing a rather dangerous mid-range sand blast attack.
Hell Lust: These Hells are extremely fast and suddenly dash in from long range to attack.
Hell Wrath: These guys don't use scythes, but instead act as walking bombs.
Hell Greed: This type of 7 Hell carries around a coffin which it uses to periodically summon other Hell reapers.
Hell Envy: This is a version of the Hell Pride that is unique to a specific area of the game.
As seen in the list above, each Hell reaper has its own particular special skill, which requires different tricks to beat it. For example, while a Hell Pride can be quickly defeated with focused ground combos, a Hell Lust's vicious attacks force the player to keep moving and stay airborne. These wildly varying fighting styles also mean that it is possible to create a variety of unique combat encounters by combining different types of 7 Hell. For example, fighting Hell Prides and Hell Greeds at the same time is a fairly straightforward affair; one must simply take down the Hell Greeds quickly by attacking them during their periods of vulnerability, while occasionally clearing out some Hell Prides if they get too numerous or too close. On the other hand, in a similar fight against Hell Greeds and Hell Lusts, it isn't so easy to ignore the Hell Lusts. In that situation, one must instead turn to more hit-and-run style tactics.
The strength of the 7 Hells is that each kind of Hell reaper is designed to be a building block for an encounter, instead of a monster that can do anything on its own. As such, even though Devil May Cry 3 is full of encounters against the 7 Hells, no two are exactly the same. At the same time, these encounters feel thematically appropriate, because the 7 Hells are share a common design paradigm.
I can confidently say that the 7 Hells are the best set of enemies from the entire Devil MAy Cry series.