How good is Daewoo k2?

Answer 1

It is an outstanding rifle - ahead of its time.
The South Koreans saw the Soviet/Chinese Kalashnikov rifle systems and the U.S. M-16 systems, and took the best of both.
The K-2 borrowed the trigger, hammer, selector, bolt, & barrel designs of the M-16. However the M-16 dumps carbon and exhaust gasses into the bolt, lower receiver groups, and virtually over the ammunition that it is getting ready to ingest. There is a belief that this causes excess heat & fatigue of the internal parts. Whether this is of great consequence is debated, but it definitely makes the M-16/M-4 system a pain to clean with burnt/baked carbon on the bolt and carrier parts.
I also, personally, had an M-16 freeze up on me in Alaska in January. The products of combustion are carbon and water vapor. Dumping carbon & water vapor on a bolt that is -30 degrees doesn't make for a good mix. - But the M-16 was designed for Viet Nam, not Alaska (or Korea).
The K-2 uses an op rod keyed to a slot in the bolt carrier. This keeps the exhaust gasses out of the receiver. It tends to give it reliability more like the AK-47 family. It definitely makes it much easier to clean after use. If I don't cheat when cleaning an AR-15 (brake cleaner), it will take an initial cleaning of over an hour, and a secondary cleaning of about 20 minutes to scrape the carbon off the bolt and out of the bolt carrier and to get the receiver & bolt group really clean. The K-2 can be, virtually, wiped down with an oily cloth and done.
Some American companies are now offering M-4 type rifles (for $1,500.00) with a gas short-stroke op-rod system, that is supposed to cure many of the M-16 ills. But it has recently come to light that this can cause a malady called "bolt carrier tilt" in which uneven forces impinged on the top-front of the bolt carrier by the op rod cause it to tilt, and can gall the upper receiver and/or buffer tube (both made of aluminum). The K-2 does not suffer from this syndrome.
Probably the biggest drawback of presently owning the K-2 is replacement parts - especially barrel parts. They are not interchangeable with AR-15 type parts. If you get a bad barrel, you're pretty-much stuck. I personally have a pre-ban that will shoot 'most anything and hold 1" groups at 100 yards. I then got a post-ban Max-200, and it was shooting 6" groups, until I tried lightweight bullets. Now, anything at 50 grains or less will stay in 3/4" at 100 yards.