I don't have an F2000 so I can't speak about it, but I have an Umarex (made by ARES) G36C and it's a really good gun for the price.
Pro's:
-Good construction (quality, solid plastic).
-The gearbox comes decently shimmed.
-There's a quick change feature for the spring that allows you to swap springs in a matter of seconds.
-There's a spring tension release feature that decompresses your spring for storage.
-Disassembly is very simple (2 pins and your gearbox/grip/trigger assembly is out of the gun); the barrel can then be swapped out with one twist.
-It has a blowback feature that can be disabled easily.
-Good consistency out of the box.
Con's:
-The only reall PITA about this gun is the mag. You can't use regular M4 mag pouches because the G36 mags are thicker and they have the little tabs that stick out to get in the way. I use Phatom Aggressor (elastic pouch) and they work great. Your other option is to get Magpul mags which are about the same size as the M4 mag (available at Ehobby). I haven't really had any feeding issues, except with high-caps.
-The hop-up unit is proprietary and I find that the stock plastic unit seems cheap. After a few months, I already see signs of some wear and tear at the nub opening when the adjustor ring rides. I have yet to find a metal version for replacement, but the plastic original one can be found. You can use common hop-up bucking without modifications.
-With the "K" version, I heard that the stock scope is useless. I have the "C" and I extended it with an aftermarket handguard so mine has a flat top with aftermarket red dot.
The iron sights were deleted since this shot was taken.