For once, I'd say ARES managed to not completely balls up a design with their G36.
True, the original batch was shocking, and was about as reliable as a Soviet nuclear power station - but the newer models (2013+) actually work quite well.
I've got one, as has a team mate. Mine is barely used, but his has seen more than 19K rounds in 6 months with no trouble. Should something break, parts are pretty easy to source.
Problems - they come out of the box with a ridiculous FPS. Mine was pushing 470FPS. The supplied magazine is a bit... crap. The iron-sights are made of a rather poor quality plastic (but they work). Other than that, it looks like a G36C, the plastic is fine (it feels similar to the real-deal), and it generally shoots where you want it to.
It's not a terrible gun (which truly is amazing for ARES) - but it's not perfect. I'd say it depends entirely on your budget - how far can you go?