Reno Jackson is a crazy new Hearthstone card. He works like this: When cast, if you have at most one copy of each card in your deck, you heal to full. You can have cards in hand, cards already used, whatever, those don't matter. So the crazy thing about Reno is that he is a heal for a potential of 29, and also he comes with a decent body. If you are playing against an aggro deck and get Reno to work, you probably just win. However, you either need to run a deck with only 1 copy of each card or accept that sometimes Reno is a big bag of bad. Neither is an ideal solution.
I have seen this firsthand - I was playing midrange hunter and my opponent managed to stall for 2 rounds by using Ice Block to be invulnerable and then dropped Reno going from 1 to 30. I couldn't come back from that position and quickly lost. It was irritating to see an opponent use a bunch of doubles of cards in her deck and then manage to get Reno to work anyhow, but sometimes you gamble big and win.
There are a lot of people trying to use Reno right now, and although occasionally they will see a huge win on that basis I think generally it is a bad play. While building a deck around Reno can generate a few huge wins against aggro it will also make your deck bad in general. Using a bunch of subpar cards with weak synergy just for the off chance at one big play will lose you more games than it wins you. Reno is strong, but sometimes your opponent is setting up to kill you when you are at 18 life and he will only be a 12 point heal. Sure that is good, but if your deck is inconsistent and full of subpar cards it won't be hard for the opponent to get that next 12 damage in and kill you anyhow.
But things change with time. Just as Secrets get more and more powerful as the total card pool grows, so does Reno Jackson. Wait a year when there are another ~300 cards in the pool and it will be a lot easier to fill a deck with really good cards without doubling anything. Just look at things like Quick Shot and Bash - not that they are overpowered or anything, but when they got released they increased the total pool of damage spells available to their respective classes and made it easier for people to load up on those. When there are twice as many cards out there Reno will be a real problem. You will still cost yourself some consistency but not as much.
Of course Reno is self correcting to some extent. He punishes full on aggro like face hunter the most, but the more control decks there are the worse Reno becomes and the less it is worth running a suboptimal deck just to fit him in. You won't see 100% of decks running 1 ofs and Reno because in that format a deck with 2 ofs and no Reno will be more powerful. It will mean though that control decks will have a singular win condition against aggro and they will be regularly running that win condition. Overall I expect it to mean that aggro will slowly lose ground over time, especially if there are any other cards that fill a similar sort of function.
Whether or not Reno is worth running right now is a tricky question to answer. However, I think it is abundantly clear that in a year Reno is going to be a star and will probably garner even more complaints than other established cards like Shredder or Dr. Boom. It is an inevitable consequence of printing more cards, just like the increased prevalence of combo decks.