Adj + 得不得了 (extremely)

"Unbelievably happy"

• Adj + (degree marker)得dedesperately serious不得了bù dé le = "extremely … (beyond words)".
• happy高兴gāo xìng(degree marker)得dedesperately serious不得了bù dé le = "thrilled / over the moon."
• A vivid, spoken way to max out an adjective.

Adj + (degree marker)得dedesperately serious不得了bù dé le

• (degree marker)得dedesperately serious不得了bù dé le piles intensity onto the adjective.

he他tāhappy高兴gāo xìngextremely得不得了de bù dé liǎo。

• happy高兴gāo xìng(degree marker)得dedesperately serious不得了bù dé le = "(he's) extremely happy."

Strong, colloquial

• Reserved for genuinely extreme feeling: rope累lèi(degree marker)得dedesperately serious不得了bù dé le, 热得rè dédesperately serious不得了bù dé le.

Recap

Read the full reference: HSK 5 grammar — Adjectives.