I'm not sure if anyone has thought about this before, but there seems to be something missing in terms of Chinese complements of degree for adjectives：
高兴得 不得了 / 坏了 / 极了 / 死了
These all take the adjective to the extreme - extremely, amazingly, wonderfully happy.
Are there adjectival complements of degree which are just a little bit happy, so... 高兴得一点儿 or 高兴得未免?
Is there an obvious reason why adjectival complements of degree only seem to be in the extreme range?!
Let's take a look of the first example:
高兴得不得了
The first 得 is a structure of emphasis. It can be translated into English structure "So A that B": "So 高兴 that 不得了（了）". Literal meaning of “不得了” is some extraordinary thing happens. For example "不得了了，房子着火了" (House is under fire). So the literal translation of 高兴得不得了 is "So happy that the happiness is extraordinary". And "so x that x" in English is never used for mild extend, instead it is for extreme extends.
Other adjectival complements are similar. You might only want to express your happiness, when the level of 高兴 exceed some kind threshold. If it is not significant, you might not even bother saying you are happy.
I will try to give you another example. Say you are dragged to a party by your roommate, but you don't want to go at all. You expect it to be super boring, but when you actually arrived there, you feel a little happy. You are surprised by this feeling: it is not what you expected. Now you want to say you are 'a little happy'. You can say "我居然有一点高兴。" Now that "有一点" makes sense. If you want to decorate the sentence to show more ironic emotion, you can say "我居然有那么一点小高兴".
You can say 相当～ to say “very”, but not to an extreme. It’s something like “bastante” in Spanish.
这盘炒饭相当美味。
This plate of fried rice is (substantially) very delicious.
You could also say 实在, which means “really quite”.
我的表哥每次考试都拿满分，实在是厉害！
My cousin always gets full marks for his examinations; that’s really quite impressive!
Is there an obvious reason why adjectival complements of degree only seem to be in the extreme range?
No, adjectival complements of degree vary. But the stronger degree is more commonly used for more powerful expression.
強 - strong
頗強 - quite strong
甚強 - very strong/ considerably strong
很強 - very strong
非常之強 - extraordinarily strong/ very strong/ extremely strong
超強 - super strong/ ultra strong
極強 - extremely strong
至強 - extremely strong/ the ultimate of strong
~
強大 - strong
頗為強大 - quite strong
相当強大 - very strong/ considerably strong
甚為強大 - very strong/ considerably strong
很強大 - very strong
非常強大 - extraordinarily strong/ very strong/ extremely strong
異常強大 - extraordinarily strong/ very strong/ extremely strong
超級強大 - super strong/ ultra strong
極之強大 - extremely strong
至為強大 - extremely strong/ the ultimate of strong
~
最(most) in 最強 (strongest) is relative. e.g. 三人之中他最強 (he is the strongest among the three of them), but he could also be considered weak compare to others
天下最強的 (the world's strongest) is an adjectival phrase
