I thought the stage battles lacked compared to the rest of the game, not because of a lack of epicness (they were degginitely incredible) but by the later stages of the game, you had to have the perfect mix of units at the perfect time, or else you were completely boned.
BUT, when it hit its stride, the stage battles became the most epic part of the game. Summoning a flaming zeppelin to crush my foes as my headbanging allies pounded them into oblivion to "Rock of Ages" remains one of the most badass moments I have EVER had in a game.
The problem I had with the stage battles was when they became less tactical mastery and badassery and more about "shit I hope he doesnt make thirty of those friggin reaper steeds that are apperently only able to be killed by me".
That being said, I loved that game, and it is in my top 10 favorite games. I just had way much more fun exploring the heavy metal wasteland blasting Motorhead in my custom built chopper than trying to lead an army of headbangers.
The only possible way they could've made it better was if they had included Iron Maiden in the soundtrack, but I dont think Iron Maiden would let them use their music.