Though I think the riddle would be easier being solved by certain gamers, still I am here, giving a try.
I guess you are
Teemo from League of Legends
Most people hate me.
According to a game forum discussion, it seemed that most players hate Teemo, some even without specific reason.
I rarely get my chance to shine.
I guess because of the fact that Teemo's abilities made it hard for players to make high damage to others.
You likely won't see me, but when you do it won't be for long.
It's because of Teemo's Camouflage ability that made him able to become stealthed easily. That's the key line for me to came up with such a champion.
I love to play. Meow.
I'm not sure about this line. Teemo looks like a cat, indeed. Maybe it is about Teemo's Yordle origin?
I have 4 forms, but only my dedicated followers see 3 of them.
I have completely no idea about this line.
I hate meeting my friends.
I got no clue from this line, either.
Alright, here's my second guess:
You are
Rengar from League of Legends
Most people hate me.
According to a discussion, Rengar is an assassin. In a PvE game such as LoL, an assassin could be a terrible teammate.
I rarely get my chance to shine.
Born as a hunter, Rengar's roll have made him suitable to ambush in the jungle, rather than fighting in the frontline.
You likely won't see me, but when you do it won't be for long.
This refers to Rengar's stealth ability, and able to kill a rival in a short period of time - especially in the late phase of game.
I love to play. Meow.
Rengar is actually a lion, in other words, a big cat. He loves challenge, a quote in the official introduction could describe:
"He feared that no worthwhile game remained, that he would never again feel the thrill of the hunt."
I have 4 forms, but only my dedicated followers see 3 of them.
It refers to Rengar's different skin. Playing Rengar require some patient, skill of moving, and the awareness of the map, so I think there was fewer player - those dedicated followers - can see his form other than the first one received. However, the fourth form is no longer available, because it came from a special event. (reference here)
I hate meeting my friends.
This may refers to the change in set-up relationship between Rengar and another champion Nidalee - once friends, yet rivals now.