In B/W, Ghetsis' Hydreigon was OP. It has Fire Blast to beat Ice and Bug types, so you cannot really counter it unless you have a strong fighting type. It does help that you can use Reshiram/Zekrom in the battle and I think Cynthia's Garchomp in Gen 4 was harder, but otherwise it was overwhelming to face Ghetsis. You pretty much have to rely on healing your Pokémon with potion and revives. You also need to come prepared to the fight by grinding a lot in Victory Road. I don't think Ghetsis was as hard to beat in B2/W2 though.
The game also has a lot of hand holding. Your rivals Cheren/Bianca guide you often and show up more frequently than in previous games. You also encounter Team Plasma at almost every city and route in Unova. In most of the Pokémon games, you normally don't encounter the villainous teams until you've earned you're first gym badge and they're less prevalent in the games. However, in Gen 5 you literally cannot walk into another location without being interrupted by Plasma like first at Accumula Town, then the Dreamyard, then the route after that, then the next town, and after that Pinwheel Forest, then Castelia and so on. You're also forced to listen to Ghetsis' long speeches throughout the game. All of these constant interruptions by Plasma and the other characters take away freedom to explore the region at your own pace.
Alder looks like he's almost a rip-off of Dakim from Pokémon Colosseum. You're forced to do a lot of grinding in to postgame in order to beat his Pokémon that are above level 70. Though it does help you're given the Lucky Egg and that you can do Audino battles in Gen 5.