I agree that Gemma is awful. She is a terrible slovenly slob. And she is at LEAST 30! I mean, I would get a 17 y.o. being like that, but she is WELL into adulthood!
And her mother is vile. Completely unhinged too. Walking around near-naked and asking Chesney to join her in bed. FFS, no woman would do that. Ridiculous.
Also the Peter-Carla 'relationship' that is on/off, on/off is so tedious now. And I am sick of so many new characters coming in, being chavvy and/or thuggish, and winding everyone up, then becoming a lovable rogue who everyone loves! 
The Rob storyline with that woman who is conveniently pregnant by him is pathetic, and I am sick of Nick Tilsley played by an actor who appears to a one-trick pony.
I also dislike the new family... (The Baileys..) Very irritating and pointless. And is ANYONE not related to the bloody Connors? Carla being Johnny's daughter was so ridiculous.
Watching Classic Corrie on ITV2 (I think) reminds me how much better it was then (1980s, and 1990's.) And before that obviously...
And most of the old stalwarts and legends have long gone... Elsie Tanner, Hilda and Stan Ogden, Eddie Yeates, Percy Sugden, Annie Walker, Ena Sharples, Albert Tatlock, Bet Lynch, Alf Roberts etc.... (tho Audrey is still there...)
I quite like some characters, like Gail and David and Sally and Rita and Audrey, and Mary and Roy, and Tracey and Steve, and Liz and Maria, and a couple of the young-ish ones like Tyrone, and the new lass Emma (Fiona Middleton's daughter,) But I am not keen on some of the rest of them.
And none of them measure up to the oldies (pre 21st century...)