Personally, while I'm ok with the old Chief, I think they did amazing in Halo 4 with showing just how human he can be. He's had his funny moments in the past, but I think Halo 4 really nailed it on the head with character development. Because funny one liners may be hilarious, especially coming from the Chief; but that's not character development. That's just some funny lines someone thought would sound hilarious coming from someone who's normally silent as a lamb.
The thing about it is that most of the funny things he says, while not feeling completely out of place, do kind of feel like someone just wanted to break up the monotony of seriousness and silence coming from the main protagonist. Chief was a very serious, by the books character most of the time in the earlier Halo games; his motives were driven by protocol and his own determination. But we see as Halo continues on, Chief stops really playing by the rules and begins to make his own decisions. That's not at all what he was taught growing up as a Spartan-II.
Halo: CE - extremely quiet, had maybe a few lines of dialogue
Deaths - many Marines, several ODST's, Captain Jacob Keyes
Problem - Flood attempting to leave Halo Ring after the Covenant fail to activate it
Solution - detonate PoA's reactor by destabilizing it making it go critical
Halo 2 - somewhat quiet, has some more humor, is barely hesitant to leave Cortana behind despite the protocol of leaving behind anything that could compromise humanity
Deaths - inconsequential as they were all Covenant (Mercy, Regret, Tartarus, Heretic leader (ex-Covenant)) along with the Marines and ODST's deployed with us
Problem - Covenant were attempting to activate Halo and Truth was leading an assault on Earth
Solution - Arbiter, Johnson, and Miranda Keyes went after Tartarus while Chief escaped on the Dreadnought to try and stop Truth
Halo 3 - roughly the same as Halo 2, but driven by his duties, however, he abandons all protocol in favor of going after Cortana. Risking everything for her; true enough, she had the Index from 04-A to set off 04-B to stop the Ark from releasing a replacement and slowing the progression of the Flood. He could have singlehandedly doomed humanity with such actions.
Death - Sgt. Johnson, Miranda Keyes, and most of the UNSC and Sangheili forces deployed with us
Problem - the Covenant are trying to set off all of the Rings at once while the Flood are trying to destroy them and take over the Galaxy
Solution - kill the Prophet of Truth, ending the Covenant and then set off 04-B prematurely so it damages the Forge on the Ark
Chief's personality was very slow to develop under these circumstances and so it was nice to see it take the steps forward it really needed in 4.
The reason i added the Problem, Deaths, and Solutions is because some times each of those had an impact on the slight progression we saw in the next game. Losing people close to him was a driving factor in his behavior I feel. The Problems and Solutions may have also changed how he looked at things when trying to stop the fall of humanity. (but that's all speculation on my part)