I think Liss is really fun to play. If you think playing a short ranged, semi-burst, heavy utility mage is fun, go for it. She takes a little getting used to, her range on her Q is sad, but you can easily poke through minions. Where she really shines is setting up ganks for your jungler. That W - R combo is ridiculous. If your jungler has any CC of his own, they won't be moving for 5 seconds. She also roams like a boss. Just make sure you run cooldown runes and purchase a cdr item to make her escape come up sooner. I've had some really awesome Liss games. She can snowball really hard. People think she's all utility but if you itemize for burst first you'll be happier.
Thresh is considered OP right now. If you like playing an aggressive support who can zone a whole team with his ult while catching someone out with his grab while simultaneously saving the life of your carry with a lantern... yeah he can do it all.