1. Speechcraft - Speechcraft, in my opinion, is absolutely worthless. At best, it is only useful for getting extra information, extra information, that is generally worthless unless the information is needed for a quest (Though even this is few and far between). You can never really fail at Speechcraft because it's always possible to lower a NPCs disposition or raise a NPCs disposition to their respective min/max values. This would be fine though if there was some sort of incentive, which there isn't. No one gives you items for liking you or vice-versa. At the end, if you want to level Speechcraft, you need to just go around town talk to everyone, and spam the mini-game. Leveling the skill doesn't come naturally, (and it's not much fun) and you'll never really level it if you try to do it only when it's needed because it's needed so rarely. I say either make Speechcraft worth having, or just scrap it. Lastly, really? Mastery perk halves bribe costs? It already costs like...an average of 40 gold, which is far less than chump change. I think the problem is that the bribe costs didn't increase/decrease with the player's default disposition score towards a particular NPC.
2. Acrobatics - Acrobatics is another skill that I find worthless. Both in Morrowind and Oblivion, there's really no need to jump. I can see it more in Morrowind at least because often you have to traverse mountainous regions, but there's no excuse for Oblivion. I can see Bethesda at least tried to make it moderately useful with Dodge and Water Jumping, but even these are flawed. First, Dodge is useless against any Marksman or Mage because you can just dodge them by strafing easily. If you're a melee character, Dodging is useless if you're fighting another melee character. The only use Dodge has is Goron-Rolling. The only place that really has a lot of water that would even remotely justify Water Jumping is around the Imperial City. Even then, you can still water-walk or just plain swim if you don't want to fast travel to there, the decreased time it takes to get there through Water Jumping is very minimal. Also, what's the point of being able to jump while attacking? There's literally no benefit to doing so other than wasting your fatigue. It's not like you're going to both dodge an attack and be able to hit them at the same time.
3. Mercentile - Oh god, please, Bethesda, please make Mercentile faster to level across the board than in Morrowind and Oblivion. I'm sorry, but I think it was an absolute horrible decision on your part to not count stacked items individually towards Mercentile. (For example, 100 items in a stack counts as 1 point towards Mercentile as opposed to 100) I'm sure you could've done something to work around exploits like purchasing arrows then selling them back.
4. Sneak attacks with Hand to Hand - It really perplexed me when I first found out that Sneak attacks with Hand to Hand don't do extra damage to an opponent's fatigue. It makes Sneak attacks pretty much worthless with Hand to Hand (Really? 66 damage and 6.5 damage done to Fatigue? Hoo-ray.)
5. Personality - I think this really ties into Speechcraft. The only incentive is to avoid combat more often, but again, this is flawed. You need to fortify your Personality attribute above 100 in order to really avoid any enemies (UESP says 180 depending on factors such as Fame). Personality certainly isn't going to help for information-gathering since, again, it's very easy to maximize a NPCs disposition. Being a shrewd diplomat doesn't help if a blabbering idiot can get the same job done.
6. Two-Handed Weapons - In my opinion, two handed weapons are subpar in comparison to one handed weapons in Oblivion. The main reason being that the amount of extra damage they do over one-handed weapons is negligible, not worth the increase in fatigue-per-swing and weight. This is more apparent with Daedric-class weapons and more end-game. Secondly, I felt that two handed weapons never really had an advantage over one handed weapons. What was the point of staggering an enemy with a power attack if you couldn't react to the staggering since you were still recovering from the swing?
7. Power attacks - Think about this for a second - 2.5 (3 if standing) times more damage for five times the fatigue cost. How does that make sense? So, instead of me just doing 2-3 swings at 1 times the fatigue cost, you want me to "waste" two swings worth of a fatigue for marginal extra damage? You can make the argument that, "It's not about the damage, it's about the chance to disarm/knockdown/paralyze." However, in all those cases, it's a mere five percent chance for it to happen. It's just not worth it, especially not with two handed weapons. I can understand if the chance was 15%, not 5%. Even then, you'll be out of fatigue, or do a lot less damage, when the power attack actually triggers the disarm/knockdown/paralyze. Why didn't work like Marksman, where it was automatic and just have each level perk overtake the last?