If you think about it, William Shatner could have gone the Leslie Neilsen route and made a career of spoof movies. During Airplane II, he was already well known for his overacting.
The opening pod door skit itself for me forgives the fact that Airplane II was not as good as the original.
If I look on the ratings in here, the first one was better than the sequel but that's not my opinion. Shatner was twice as funny as Nielson was and his bit was memorable. 'Let's get out of here, close it up,lights out!'' Hilarious! I give 7/10 to the sequel. 6.5/10 for the original.
He plays spoof perfectly because he's so naturally over-the-top. It's a side effect of William Shatner's years of stage acting, he's so hyper dramatic that he's hilarious to watch, and he plays on it. Shatner's a rival for Leslie Nelson for sure, and they could have easily swapped roles in Forbidden Planet and Star Trek. Leslie Nelson plays his roles a little more seriously, he's hammy and over-the-top in a more subdued manner, but Shatner has a wider dramatic range. Both are awesome in these Airplane movies!