A-1's got a pretty good reputation under their belt. And keep in mind they've got Sony and Aniplex to back them up. I can guarantee it'll be much better than Sunrise's attempt back in '07. Here's a list of some of there previous stuff not including some other shows they have planned to come out later this year:
* Zenmai Zamurai (co-production with No Side; 2006–2010)
* Ōkiku Furikabutte (2007)
* Robby & Kerobby (2007)
* El Cazador de la Bruja (original production: Bee Train; finish animation, 2007)
* Persona -trinity soul- (2008)
* Tetsuwan Birdy: Decode (2008)
* Kannagi (2008)
* Kuroshitsuji (2008)
* Valkyria Chronicles (2009)
* Fairy Tail (Co-production with Satelight; 2009–present)
* Working!! (2010)
* So Ra No Wo To (2010)[6]
* Ōkiku Furikabutte ~Natsu no Taikai-hen~ (2010)
* Senkou no Night Raid (2010)[6]
* Togainu no Chi (2010)
* Kuroshitsuji II (2010)
* Seikimatsu Occult Gakuin (2010) [6]
* Fractale (2011)
* Ao no Exorcist (2011)
* Ano Hi Mita Hana no Namae o Bokutachi wa Mada Shiranai (2011)
Also I managed to get a hold of a summer anime list and i don't see iDOLM@STER on it i guess this means they might be aiming for a fall release. However that could change and a summer release could be possible since this is only an early list I've found and iDOLM@STER's date has still been unannounced.
http://media.animevice.com/uploads/0/5262/382534-1301268073241.jpg