The Samsung Galaxy S II hardware is kind of plasticky and so is the Samsung Galaxy S III, I agree. One of my friends has the former and another has the latter. They are still well put together phones. It is not a huge issue for me because I usually put TPU cases on my devices anyway.
The only issue that the friend with the Samsung Galaxy S II has had is that the GPS is slow to lock on and it does not maintain lock very well at times. Ever since he went to Android 4.0 and then Android 4.1, it has been pretty bad, and so has the battery drain. I keep telling him to try AOSP ROMs, like CyanogenMod 9 or CyanogenMod 10, but he likes TouchWiz, I guess. That is his choice and TouchWiz is not terrible as it once was. My other friend, the one with the Samsung Galaxy S III, recently switched to CyanogenMod 10 and he likes it a lot. If I get a Samsung Galaxy S IV, I would most likely go to stock AOSP ROMs pretty fast, and then try newer builds of TouchWiz as they come along.
Nokia 638 > Motorola Talkabout > Motorola V60t > Motorola V60i > Motorola V505 > Samsung Epix > HTC Hero
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