Extreme degree: 极了, 死了

For a maxed-out degree, after the adjective you add 极了 ("extremely…") or, more colloquial and over-the-top, 死了 ("…to death"): 好极了 = "fantastic!"; 累死了 = "dead tired". They go after the adjective, unlike 很/太 which go before. 死了 sounds strong and informal.