You know, I still haven't got an answer what there is that can only be done with attributes...
Well, first of all the absence of attributes leads to the fact that every character in Skyrim, no matter what armor he is wearing, will eventually travel at the same speed, which is, quite frankly, [censored].
Secondly, many effects that could be achieved by simply focussing on a certain main attribute, can now only be achieved by either armor entchantment or a specific perk in a specific tree. So in order to get more magic resistance (Willpower in the old system) in skyrim you basically need to train Alteration to at least lvl 30 and put at least 3 perks into that tree. No matter if it fits your character or not. This is nothing less than a restriction - gameplay wise.
The alternative would be to train enchantment and waste enchantment slots on your armor. The old system had more options for achieving said effect. Same goes for magica regeneration.
Charisma would allow you to not only influence people, in Skyrim there is no such thing as "influencing people" except for very few occasions when the game thinks it's appropriate. People would actually refuse talking to you under certain circumstances and you could actually haggle, which, again, in Skyrim is not possible anymore. Prices are set, depending on your speech skill (which btw increases passively as you buy/sell items).
Again, less options, more predetermined stuff.
Agility would be one factor that determines your chance to hit an enemy with bows. In Oblivion ans Skyrim every character, no matter what profession, is a perfect archer by default. Same goes for melee weapons and for spells. In Skyrim your magica is the only factor that decides wheter you can cast a spell or not. By that logic even a Skeever could summon a dremora lord if you gave him enough fortify magica potions.
Main attributes determined (along with skills) whether you could join a guild/ get promoted in a guild. In Skyrim it literally doesnt matter what profession you have, you can become the leader of every single guild.
That is only a small selection of what was taken away by taking away main attributes. I wonder how you can not see the obvious simplification that is the result of the new skill/perk system.
Of course it's a matter of taste and I'm sure many people are actually glad with the way the series has changed. There is, however, no point in arguing that the series has become less complex and thus, for many people, less enjoyable.