Poor loss, mainly due from the lack of experience in playing these kind of players in these kind of matches.
It's hard to acknowledge for us atm, but Jo is critically limited in his performance by his lack of experience : he is 24 and has played two wimbledon and one RG in his entire life. He hasn't even played one fifth set. Compare it with the experience of the other top players like Murray or Djokovic and it's telling.
Next year period of Rg and Wimbledon should be very interesting though, particularly RG : he has gone further on clay, than on grass after all.
Fortunately, he is a much experience player on hard, so this US open should be good. I just hope that this time, he is going to play a lot of tournaments before. He should know by now that he needs some practice to be good.
I'm aware of it rationally, he's played fewer tournaments than any 20-year old I know, but at the same time he puts together such amazing displays and results, it takes over. Karlovic is a special breed and a lot boils down to patience, waiting for your opportunity and not getting frustrated, as well as not going for too much when you do because outside the serve he's not your typical top class opponent. At times, I felt he was actually more frustrated by lack of anything to get pumped about, than the nonreturnable serves. Perhaps that pumped up state is when he's "conditioned" to play clutch (I really thought the break in the 3rd was totally uncharacteristic for him, he practically gave it away on his own). As it is, there were very few points he got excited about in the sense I'm getting into the grove, because there was very little play on either serve.