Most people would have you believe that the stage battles in Brutal Legend are badly done RTS sections in a game made up of other little mini-sections. And despite the fact that this seems to be the overwhelming majority's opinion, these people are, and always will be, absolutely wrong.
 
I'll try to explain. What Brutal Legend was originally supposed to be was a multiplayer war between different factions of metal. And that game still exists, very polished and complete, in the final release of Brutal Legend. However, along the way, Double Fine were requested by their publishers to expand the single player more and more into an action adventure game in the vein of Zelda. This isn't necessarily a bad thing on its own, but Double Fine had spent the first two years of development exclusively polishing the core mechanics of the game. This is a game focused around a new type of battle gameplay, where you can command troops like an RTS but also get down in the action yourself, and drive any car you make, ride any beast you build. Trying to twist that multiplayer-focused, very mechanically polished machine into a single player game wasn't entirely successful.
 
So what they ended up doing was making the single player into a tutorial for the multiplayer. The core gameplay is fairly complex and combines elements in ways that no other game has done before, so it makes sense that a lot of explaining would be needed. So they broke it down - first bit of fighting on foot to show the player how they could fight weak infantry on their own. Then an introduction to the unit commands where they're shown how they can tell troops to do one thing while they do another. Then a mission where they're introduced to the Double Team attack and shown how it protects the player from any damage as long as the unit they're DTing with survives. Then another Double Team focused mission, showing them a very important Double Team - the stun attack of the Thunderhog. Then they're put into a battle and expected to use all that they've learned to claim victory.
 
But unfortunately, that isn't what most players did. Instead of thinking of the game as 'Mechanic 1 Tutorial', 'Mechanic 2 Tutorial', 'Mechanic 3 Tutorial', 'Full Gameplay Section', they believed that the stage battles were simply another simple 'mini-game' - first a Hack And Slash Section, then a Unit Commanding Section, then a Vehicle Section, now an RTS Section. So they completely forgot everything they'd learned from the game previously, putting it in an entirely separate compartment in their head, and focusing entirely on the two new elements that had been introduced - the ability to make troops at will, and the fan geysers to control - rather than realizing that the stage battles were in fact the 'everything sections', where the gameplay comes together as a whole.
 
And unsurprisingly, when you play a game by ignoring 90% of its mechanics and expecting it to hold up entirely on the one that you're using, it doesn't play well. Complaints like "you can only command a whole group!" or "the individual orders are really clunky!" or "there aren't any hotkeys or a minimap!" all arise from misunderstanding the game and playing it wrong as a result. Try playing Halo by only meleeing people and never shooting, or throwing grenades, or even jumping - you'll probably find that it's difficult and frustrating, you'll complain that there's only one type of punch and you have to change guns to do a different one, and that compared to the likes of Street Fighter it's just not a very good example of the fighting game genre. And doing that would be equally as ridiculous as the way most people played Brutal Legend.
 
Yes, I'm serious. Try the game again, but this time actually USE the Double Team attacks. Actually USE your guitar solos. Actually USE the combat, and your car. And you'll find that suddenly all your previous complaints about the game not being a very good RTS will disappear because it's not, and never was, meant to be played like an RTS.