For example, I just got done playing a game of Morgana support. Prior to this, I've tried her out once as support, but felt that she was lackluster, and that she wasn't my style. On a whim I tried playing her again, as the enemy first picked Thresh (my primary support). It ended up being one of the most fun games of support I've had recently.
So who did you try out a second time and realize that you were missing out?
At first I thought Garen was worthless because of the rising mobility creep, but now I realize the wonders of hiding in a bush. Silence OP!
I have to say Quinn 
. Like I hear on the forums and the community beta that she has too much stuff loaded into her kit, she is not up to par with her visuals and stuff like that. But when I bought her and played her, It was the most fun I've had since URF. I love everything about her and Valor. Plus her skins are extremely well done. Quinn is now one of my favorite champions
The first time I played Lucian (during free week), I wasn't really sure what he was supposed to do - all of his abilities just felt like 'Press this to do damage,' which was a major turn off. I thought that Caitlyn was a better lane bully, Jinx outscaled him, and basically every ADC had more utility. It wasn't until I bought him and started seriously trying to learn him that I began to appreciate the power of his passive and ultimate in sieges, and how frickin' hard it is to stop him from doing damage in teamfights. Now, he's basically the only ADC I feel comfortable playing.
Vayne. Before I was terrible at CSing so obviously I didn't understand her. Plus my only mindset was that autoattacks didn't matter and the only way to win was heavy casting, boy was I a fool. Months later I tried her again, once I fully appreciated the role of ADC and that nukes aren't everything, now I love her. I mean, I still love my mixed AD casters like Corki and Kog (at least the way I play him), but I can now appreciate auto based ADCs.
I originally really disliked Kha'zix when I first started playing League, mainly because I was new to jungling and lacked proper mechanics and game knowledge, so I figured he was just awful or not my style of champion. After playing for a few more months and adapting into the jungle and learning a lot more about the game and champions themselves, I thought I'd try it again and ended up being able to hard carry quite a few games, or at the very least have a lot of fun.
mundo support, i am currently 15/1 with him in normals.
Oh man, where to start.
Twisted Fate is the first that comes to mind. He was actually the first champ I bought, and I was never able to do well with him because of my own inexperience and promtly left him in storage. Then I came back to him with proper knowledge of lane pushing and ganking and used his ult to massive effect.
Teemo, I guess, was another one. He just seemed to be a minor annoyance when I first played him, then I played against a teemo who knew how to use his kit properly and realized he could be very effective.
Karma is probably the most recent. She was a sleeper for me up until I saw a friend of mine go 2v1 bot lane with her and hold his own (he might even be reading this right now if he remembers the shaco-twitch game). Ever since I've realized how great she can be, hell I didn't even realize her ult decreased cooldown on autos until my 6th or so game with her after I brought her back. Been trying Karma Top since then and it's been a quite enjoyable change of pace for me, as well as a nice counter pick if I feel the need.
I still need to try full-damage Darius, I used to play him really tanky but I've been crushed by enough (after a few unfriendly ganks) to realize how snowbally he can get.
Kog maw, for the longest time I felt that Kog just couldnt cut it anymore. He was just to easy to reach and to weak during the early game. Then I tried him ap mid after Q changed to a skill shot... went in expecting to be the reason we lose... came out the reason we won. Been rocking ap kog as my main mid laner ever since. Even though his early game is weak, the insanely powerful yet surprisingly inexpensive build combined with his range and utility thanks to e in team fights make him a force to be reckoned with. His tower taking is top notch almongside his pushing power. He can siege with the best of em and then some. his gate is his move speed, but 3 MS quints fixes that right quick.
I felt Taric was weak when i first played him but after i watched a youtube video on his update i tried him again and now i feel i can compete with top supports like leona,thresh,and even braum but morgana is still hard to fight because of her spell shield.
Tons of champs when I was starting out i had misconceptions about but the first champ I think I didn't really care for was Janna, her mechanics were really confusing to me so I didn't like her that much, that's not the case anymore she's one of my favorite supports now
I was stuck playing tank build on her for awhile and it never really clicked me with me enough. Once I started playing AD heavy early game on her and going 21/9/0 she felt so much more right and fun to play.
I played Talon in dominion once, hated him, and thought his passive didn't do much. He is now one of my 3 favorite champs.
Thought he was just a smash your keyboard champion but actually found him quite fun.
when I bought olaf like 8 or 9 months ago I thought he was a lot harder than he actually was. I just could not get the hang of his passive he was the third champ I bought with the other two being warwaick and udyr. until recently I got used to his play style, pretty much dive the carry and ult when cc'd.
I remember my first time tryndamere.... boy those are some bad memories. Full Tank Trynd ftw?
Playing Rammus jungle. First item? Rabadon's Deathcap >_>
Shaco.
I saw somebody play him once; I bought him and sucked.
I didn't touch him until 5 months later, when I built him AP and wrecked face [=
. First time I ever played her I just felt she was crap, but now she's one of my most played champions
Then i first played Akali i thought she was lacking damage, and i mean, a LOT of damage. but at the same time i saw her go 21-0 in games and was like "HOW!! SHE'S TERRIBLE" then my friend showed me how i Should be playing her aaand Overpowered....
For Me the champ was 
, I saw the champion spotlight for her and decided to pick her up. At first I could not get the hang of Q'ing before ult, so I kind of ignored her and just let her sit in my champion pool and claim it to be a bad buy. But I was playing some dominion with a friend and I got this crazy idea to play her, and I destroyed with her. Now if I'm ever on a big loosing streak, I just play a game of Diana mid. best mid lane mage/fighter/assassin.
So i tried ez i sucked miserably then several months later it still havent changed besides that i feed a little less
I don't know if this quite counts. But when I first tried 
while she was free, I rocked with her. Then I bought her a few months later, and suddenly couldn't do anything at all with her. Took me a while, but I stuck with it, and now I've actually had a couple people compliment me as one of the best players they've seen.
I did something similar with 
. When I first tried him, I thought he kinda sucked. I wasn't very good with tanky characters, or melee champs in general. But I've always loved the monkey king legends, and after Instalok published their 'Blukong' video, I decided to give him another try.
A couple of guides later, and I'm stomping all over the top lane. And I don't plan on leaving :p
Alistar. I am playing mostly with friends, and when I was still unexperienced Summoner (early S3), I decided to try Alistar (hey, he is free!). Game gone horrible wrong from my side (it later turned out that I had all runes wrong for tanky support, as I was maining poke supports) and my friends (especially one) weren't allowing me to pick him up for a long time. After few months I decided to practice with him on bots, and later try him in pvp (when that particular one friend wasn't playing). It turned glorious and Alistar become my best (and most appreciated by my friends) support in S3.
Another story is the first game in Pre-season 4 with over-the-top assists gold and awesome Talisman. Had most gold in the entire match as support Alistar :D
Definitely 
. I thought he was a decent tank, but couldn't hold up in the current meta but with sooo many Rioters mentioning him as an example of off-meta tank junglers that are just underrated currently I decided to give him a shot. I've never had so much fun dueling 
or 
or 
because I'm too tanky for them to kill but they just. can't. get. away.
Also 
. The first time I played against him, I called him a BS champ that just facerolls in lane until his mana runs out and requires no skill. Now that I've played as him a couple times, I see him as...a BS champ that just facerolls in lane until his mana runs out and requires no skill...but is kind of fun to play as?
