I've mostly played Warhammer in which "everyone is special so no one is special" -- most units have standard bearers and musicians, they have a small benefit (+1 to combat resolution if I remember correctly). In Havoc - Musicians are game changers. They give the commander (you) the ability to pass on orders - just like in real life! This is the first game I've ever seen that musicians really have a purpose. (In fact, they might be too good!)
Standard Bearers, likewise, inspire your troops to fight better. A force without a standard facing off against a force with one is actually at a pretty big disadvantage. But woe betide the force that loses their standard to the enemy! Protect it well or your forces may well flee the field (figuratively).
Speaking of which, Havoc doesn't have a morale system. Now, normally I find morale systems necessary and fun. But Havoc doesn't really need it and adding it wouldn't add anything. At every game I've played it's been obvious when a force had reached its breaking point. It's a bit like chess - you know when you're beaten and you resign the game. You could drag it on and play it out but why not just resign the game and start a new one? Because of the One List, it's easy to tell that your two remaining Melee and Shields aren't going to be much of a match for the 3 remaining Great Weapons your enemy has.
The One List. It's the dragon in the room, so let's talk about it. I suppose you will either hate it or love it. I've seen people decry the game (without ever having played it!) for not having rules specific to fantasy races. Dwarves shouldn't have the same movement as humans, elves should be masters of the bow, etc.. But in return for not having those race-specific rules --- you get to use any miniatures you want. My wife has put together a force of centaurs, mermaids, fairies and...well, I'm not even sure what a couple of them are! And her list is equally competitive with my High Men based on a Warhammer Empire army. Not only competitive - but automatically balanced. So I guess the question is - do you want to play Warhammer where only specific units are statted out and there are always cries about the latest cheese army -- or do you want to learn one set of rules, One List and play lots of different forces using every fantasy miniature you've ever conceived of?
That's a bit of a straw-man argument, of course. There's nothing to keep the Warhammer player from saying that Mermaids "count as" orcs. But it's the elegance of the ruleset that really encourages that kind of innovation and creativity in Havoc.
Elegance - when was the last time you really enjoyed reading a wargame rule book? When was the last time you saw sportsmanship embodied in a rule(Peter Pig does it - I can't think of any others)? When you read Havoc, you really get drawn into the spirit of the game -- which basically boils down to 3 things: Inclusion, sportsmanship and fun. And it provides fun in spades.
My one ruleset to rule them all? Yeah, I really think it is. It's got everything I want. Is it without flaw? No - there are some odd holes in the rules. For instance, while there is a lot written about how to match up multiple combats, there is nothing that actually explains how to fight one out. (Common sense guided us through, but guidance and an example would have been appreciated.) Spell usage for Magus are begging for the expansion that the core rulebook says is coming soon...but that was 5 years ago. And while the Giant gets 3 pages of description, fantasy staples such as a Dragon are lumped under Behemoths. It's not too bad to build a Dragon -- make it a Flying Behemoth (flying rules are under Knights Furioso, covering any flying steed), but some guidelines for giving that a points cost would be nice. (Not a formula - just a guideline. "Flying" ability for a Behemoth is way different than "Flying" for a horse (Pegasus))
In other words - most of my flaws are just in wanting more, more, more. It's a bit like Full Thrust that way. The basic game is simple and understandable and fairly well-balanced. So people started tacking on more and more of the things they loved. Havoc is the same way. I want Dragons so I'm going to add a Dragon type. I've already considered an "Elite" type for, yes, Elven archers which simply adds a die to the Ranged attack. Or Paladins who add a die to melee against undead.
But the only reason I'm considering that is that the core game rules provide such a strong foundation that I think that bolting those things on won't appreciably affect the game. And that's why I love Havoc.
Seriously - give it a try.