I first got to see Solstice Arena, Zynga's latest iOS entry, at GDC earlier this year, and then had a short meeting again last week with the publisher at E3. But you no longer have to take my word on what it's like: The game arrived on iOS worldwide last week, so you can grab the free-to-download title at your leisure.
And I recommend you do. Zynga has a reputation for pushy freemium elements in goofy casual titles, but I can confirm this game has none of that. This is a true mobile MOBA (multiplayer online battle arena) title, similar to League of Legends, but very iOS-centric in its delivery. The game has been simplified in a lot of very smart ways, producing a high-quality title that's very impressive. In my own play, I've found some minor balance issues (the healer character, for example, seems awfully overpowered, especially when teamed up with a burly bruiser), but I am sure those will get evened out as the game gets periodic updates and tweaks.
And while yes, this is a freemium title, that part is also done very intelligently. The freemium elements are mostly confined to customization and convenience. Just like League of Legends, the game opens up a number of free heroes to play every week, so there's ongoing variety even if you never spend a dime. And if you do, real money can only buy you custom skins for the heroes you own, or can pay for boosts in your own XP, so spending money doesn't affect the gameplay at all. Prices are a bit high (which is something else I expect will likely be tweaked in a future update), but all in all, the freemium elements almost never get in the way of the gameplay, which is very respectable on Zynga's part.
In short, Solstice Arena is exactly the kind of game Zynga needs to help cleanse its reputation as a money-grabbing casual publisher. I would hesitate to call it truly hardcore (I think the game needs about double the heroes and maybe another map or mode to really start comparing its depth to a standard PC MOBA), but it's definitely a "mid-core" experience that delivers a lot of fun. If you're a MOBA fan or just want to see what Zynga is doing right lately, give it a download and a try on iPhone or iPad.