Every gbbr brand has some sort of issue with it intrinsically; it all depends on how much you're willing to tolerate or fix it that depends on whether it is a good GBBR to you.
The WE M4, before I worked out all the quirks with my GHK M4, was my favourite GBBR. It shoots laser accurate, the mags are durable, and the aftermarket parts are plentiful to your heart's content.
pros:
-very accurate with or without upgrading inner barrel and hop up
-most parts are 1 to 1 milspec so you can actually purchase real steel items without issue (if you feel inclined to more realism and authenticity to your rifle)
-economically the best in comparing price/performance/quality (goes out the door once you get hooked and buy every upgrade for it
)
cons:
-pot metal internals will degrade over time, warranting replacement or upgrading to steel parts. (main culprits: bolt catch, bolt carrier, firing pin, auto sear)
-if you didn't know these main issues, then you could get easily frustrated on issues like no lock-back on last round, or firing-pin-dead-click
Once you know how to mitigate these main problem areas, then the rifle is very reliable. I think the important part here is how passionate will you be fixing it when something goes wrong with it.
Bottom line, if you like the idea of the mechanics of a GBBR akin to real steel guns, then you should have no problem and enjoy your time. But if you're not the troubleshooting type or like to get their hands dirty, then it might not be for you.
Mind you, that is not exclusive to the WE M4 and will be the same for any GBBR brand.
tl;dr
I say your first venture into GBBR will be a good choice with the WE M4.