They essentially force you into their 3 roles. How can you be a battle mage, by all means tell me? In oblivion I had a mace and shield and was able to cast spells. In skyrim, i have to constantly pause combat to switch between shield and fireball. They also removed touch spells as well. Common example why mainstreaming is not a good thing in this case.
A battlemage just means using spells, weapons and armor. You don't have to be using a shield AND sword AND spell all at the same time. And sheathe your sword, don't ditch the shield. Keep the shield up, put fireball in your left hand - you can't swing a sword and shoot fireballs simultaneously - shoot the fireball then draw the sword again.
You are in no way forced to play only a warrior, thief or mage. That's just baseless nonsense. You can be a barbarian swinging a two-handed sword with light armor. You can be an illusionist-thief, casting muffle and invisibility to sneak around and steal things. You can easily be a necromancer/firemage/warrior who summons a Daedra to assist in combat, fires off firebolt spells, then casts firecloak and draws a sword for melee combat. All of these are entirely viable. There's simply nothing forcing you into only three ways to play. A zillion people here could tell you they have characters who don't fit neatly into those three types.
I don't know why they didn't incorporate some kind of system where your class isn't a set definition, but evolves on your playstyle and changes in your playstyle, rather than just be rid of the whole thing. Starting out every player could have the generic "adventurer" class. Suppose a player earnes the title "warrior" in low levels, but say midway through the playthrough he decides to incorporate magic into his work. He's no longer a "warrior." Now the game, as well as other NPCs call him "spellsword" or "battlemage." The perks and perk trees could easily be part of this system as well.
But what's the point of having a little box in a menu that says "Class: warrior" at all? What does that get you? Just use weapons, magic, and stealth as you see fit, in any combination you wish. If you want to be a warrior, then
go be a warrior. If you want to be a necromancer-battlemage, then go do that.