Patch preview and season 2 mastery changes(!) are out, definitely look into them on leagueoflegends.com
Mastery changes are pretty game changing and I am unbelievably frustrated about Riot inexplicably not making a calculator tool with this to theory a little easier on but it'll be interesting to see how it plays out. The one mastery concept that really seems to have gotten destroyed is the 9/0/21 AP carry thing (even though most of the stuff that build takes now is still there), since now there's actually a reasonable opportunity cost in deep offense than AP carries probably won't be able to give up.
Jungle mastery choices are interesting to me though I overreacted to it a bit in the original edit of this post. The current 1/13/16-type builds get to keep most of their utility in something like 0/21/9 since Swiftness moved down to tier 2, the buff mastery seems to be one rank now(can't tell since it's scrolled off the side of the page...), and the Smite mastery moved to defense, which is a big help to the tankier jungler that are sort of running the competitive scene right now like Udyr, Trundle, and the recent Rammus resurgence. While most people build them tankier in the jungle anyway I'm curious what people will end up running on Gangplank, Nocturne, and especially Lee Sin since they don't fit in that archetype as well, though they could all survive running 0 defense (I think that the difference between a tank that's actually deep in defense vs. these guys just added atmogs midgame might start to be more meaningful, though). All the junglers are likely to lose the experience talent from support which messes with a bunch of routes, but I imagine Lee Sin at least will continue to mostly run 21/0/9 and ends up with slight damage buffs. Wonder if the new mastery set-up won't actually open the door for some new junglers since Butcher and Tough Skin are both tier 1... 19/2/9 might be fun for the Lee Sin types because of it, Executioner seems awfully gimmicky by comparison.
Some random interesting talents I'll enjoy seeing the effects of like the starting gold bonus in support, the tower siege related talents in offense and defense, the bonus gold on kill/assist talents in defense but not the hilarious xp one in support(wtf...), and that thornmail light for minions talent in defense (which is sort of a joke but it really will cut a couple seconds off Wraiths and Wolves for a lot of Junglers during the first clear or two). Most builds losing the experience talent (now points 13-16 in Support) interesting. Wishing Support could get away with 0/21/9 to break up monotony but imagining it won't happen because of Greed being a 3 pointer now if nothing else... maybe 0/19/11 for Mercenary + Greed?
Lot of ambiguous nerfs/buffs in the patch preview to keep us on our toes but the most interesting one is Caitlyn, Graves, and Kog'Maw getting ambiguous nerfs and Tristana, Corki, and MF getting ambiguous buffs to try to bring all the AD carries in line. I'm not really sure I agree with Riots perception here if I interpret that to mean they kind of have the AD carries tiered OP: Graves Kog'Maw Caitlyn Balanced: Ashe Vayne UP: Tristana Corki MF Burn in Hell: Twitch... I'm glad to see MF and kind of Corki getting some love but I thought Tristana was fine to begin with (though changing her abilities to actually scale off AD and nerfing her steroid a bit would modernize her nicely if that's more what they do) and Corki was at least close to being a competitively viable pick so I wonder if the two of them won't end up being the next FOTM. I think Caitlyn is a little overrated in that she's probably the worst AD in the game after 20 minutes if her lane opponent doesn't give her anything easy and manages to stay in her ballpark farming and given that Ashe basically fell off the planet after Dreamhack I'm a little surprised she went without a mention. Assuming the changes are relatively small in all directions it should make the AD field dramatically more balanced though, looking forward to it and will probably finally buy MF with that triple pack(even though I own Kat and will never play Xin...) because of it. She's the coolest AD anyway I have a nonironic gay video game crush on Graves but she can totally be my #2 if they nerf Kog substantially.
Concerns about the execution aside you have to give Riot credit for their hit list this patch: rebalancing ADs, AP Sion, Sona, hitting FOTM pretty well there. Outside of their weird hatred of nerfing AP assassins they got everyone I expected them to... except Xerath. Boggle...