Since April 2011, I've owned an Ares G36c. So it's been about 7 months. I estimate I've shot about 12,000 rounds through it. So far the only thing that has broken was the tappet plate spring. I replaced it with a version 3 spring.
So far it's been pretty good to me. I can't say anything about it's quality compared to other brands, since the only other gun I had was a cheap Aftermath M4.
I agree that parts are hard to find from retailers, but I've been able to get the following parts directly from Ares Customer Service:
G36 ball bearing spring guide (SG-01)
Nut that screws into ball bearing spring guide (part F48)
G36 flash hider (FH-G36-01)
G36 to M16 Magazine Adapter (G36-11)
G36 140 rounds magazine box set 5pcs/box (G36-140P)