Yeah I think Korea is a pretty strong civ. I wouldn't say they are overpowered but I'd be putting them as top tier for sure. It may be just because they are new and I kind of like them but I feel they may be among the top 2 or 3 civs in my books at least.
Their free tech boost thing is good but I don't feel its overpowered. It is too early to state that for sure, of course. My feeling is though that the very early tech boosts don't amount to very much.
Consider the library. If you build it (or the GL) early as most people do, you will get about 50

as your boost. Nice but hardly game breaking. If you delay the library in the hopes of getting more free science, you are losing out on the library bonus itself for quite a long time. You would've been further ahead to have just tried to get the GL like any other civ and get a full free tech of your choice. So that part hardly seems overpowered.
A similar argument can be made for the NC. If you delay it, sure your boost will be more but you are losing a lot of

by the delay. So again I don't see a great deal of advantage to the delay. Again you might be able to net 75 - 100

here is my feeling from the UA.
So then it turns to the latter ones. The university can be tailored to grab you a nice beaker chunk. Again it's nothing you want to delay too long as you are missing out on running scientists and hence generating GSes and such... but you can get another nice chunk of free beakers.
The later ones of course you can tailor just like regular RAs. However at that point getting a free RA is nice but hardly game breaking. So my feeling is they actually did a good job here making it nice but not too overpowered.
The actual scientists are pretty darn impressive though! Each one generates 5

which in your capital translates into 9.15

. So you almost get 20 extra with running 2 in the capital. That's very nice! In fact even running engineers for the science seems like it might be efficient, especially if you want to generate a GE.
One thing I never expected (but should have) is you get that science from the unemployed people too. Not sure that's all that useful but if you have some crazy grassland food start with no production, those unemployed people might be able to push science forward and boost production a touch. Not exactly a goto option but might be something to consider if you really want that tech 2 or 3 turns earlier (like say to bulb something with the GL)
EDIT: Oh yeah.. forgot... regarding the exploit. Yeah it's completely insane. Think about combining it with mercantilism and Big Ben... who needs friends for RAs? Why help the other civs out? Just spam your own... they never get broken! It's definitely on my not to use list of exploits
